One PieceForming
This theory posits that Eustass Kidd is the inheritor of Rocks' will, based on details from Film BAAD, and will be Luffy's true rival throughout the series.
The Film BAAD is about the return of Eustass Kid, giving a full detail of his backstory, motivations, and most importantly proving he is the inheritor of Rock's will, juxtaposing him as Luffy's true rival for the series.
My first point, is that Kid and Rocks share a striking amount of similarities in the same way Luffy does with Roger. Kid's smile while facing Big Mom is the exact same as Rock's when he faces Imu for the first time as seen in the first two images on the board. Normally this could just be a coincidence or a case of the mangaka simply drawing inspiration from himself, but in a series like One Piece where laughs and smiles are everything for a character, this is especially notable. Especially when both times they smile at the strongest person they have faced directly up to that point, same situation same expression. The fact their careless grin while facing what could be death is the EXACT same, when Rock's exact grin is something only Garp, Whitebeard, Gaban, and Rayleigh alongside those who survived God's valley could know about is futher proof of this suspicion.
Chapter referenceChapter 1163Rocks is smiling with the exact same smile as Kidd's despite their different head shape
Chapter referenceChapter 1039Kidd shares the same smile as Rocks while bringing down Big Mom
Here, I'll go over how much Blackbeard and Rocks differ, and why Blackbeard cannot be and should not be the sole inheritor of his Father's will. Leaving no one to truly inherit such will randomly. Loki met Rocks, meaning he instils his mannerisms from what he saw, not who Rocks is. Honestly he parralells Shanks, something Oda may intentionally drawing on to explore during the final war when Shanks arrives. Regardless, the fact Loki is unable to draw someone as weak as pre Dressrossa Hadrudin to his side at any point in time with at least his strength, is further suggestion of the lack of similarities between him and Rocks. He wants to be like Rocks but clearly is not, as the strognest giant after Herald died was willingly imprisoned, instead of being mad enough to fight out of the chains like Rocks would in the same scenario. He is the apprentice who can recognize the true carrier of that will after seeing it himself, baring witness like Shanks did. If Blackbeard is the failed imitiation (Ace) and Loki is the Shanks to Rock's will, then Kidd is Rock's Luffy.
Just because a child prince is being spoiled and not listening to him, Rocks gives him a full blown possibly haki infused attack. In comparison, Blackbeard is caught so off guard by a child being on the battlefield after his life, he is caught off guard and forced into the defensive position shown in 1059. Rocks sees any man, woman, or child questioning his authority as a threat, while Blackbeard only seeks the right moment before making any big move. Rocks is challenged to a duel by a child? He stabs him. By the secret King of the entire world? He threatens him first. Blackbeard is threatened by a mere former Admiral in Akoji, and he is on the backfoot apologizing. The reason so many legendary Pirates are drawn to Luffy is because of his exact similarities to Roger. Rocks and Roger being the only pirates with major characters who inherited their will despite no prior connection also makes sense logically, as they are the only remembered pirates who took the world by storm as they died, who did not only die three years ago but longer than that. Giving time for those who inhirited their will time to grow from sprouts to collosal forces that could change the world.
Chapter referenceChapter 1059Blackbeard is offguard at the sight of a child Pacifista on the battlefiled trying to kill him
Chapter referenceChapter 1155Rocks one shots child Loki for simply not listening to his orders, despite plans to recruit his Dad
Blackbeard shares none of those similarities and neither does Buggy, the only other character in the series people compare to Rocks besides Kid. Even IF Buggy is Rock's son, Buggy is not ruthless or particularly strong now or will be later in the series. The thing that makes him endearing is the strength of his weakness, it's what lets him fail upwards. Buggy suddenly being at the level of Rocks, Luffy, or Shanks by the end of the series makes no sense. If he had half the aptitude of Shanks, he would have at least the basics of haki known/mastered after spending years with such a strong crew, yet he does not. For further evidence of the importance of exact not relative similarities, I have another picture of Rayleigh reminicing on what Shank's told him of Luffy here.
Chapter referenceChapter 506Shanks is excited over Luffy saying 'the same words as the captain, the very same'
Blackbeard's only similarity to Rocks are from stories told to him from his Mother and his prior knowledge of Imu, he carries the same ambition, but the will behind it is different.
A question you could have after these points, is how would Kid even if he is Rock's succesor possibly recover after getting his ship destroyed? He has no fleet, and it's questionable if he is even alive after the divine departure and Dorry and Broggy's combined attack. To that, we know Kidd survived the divine departure, and as for the Ikkokou Soveringity attack, this is the same Kidd who survived the most direct hits from an emperor out of any of the trio of Law, Kidd, and Luffy (without regen in between) while also having been stabbed and nerfed by Hawkins. Before the nerf Kidd was capable of pinning Big Mom down by himself well after she noticed him by using one metal arm, showing how strong pre nerfed Kidd actually was. All these feats will be shown below as they are especially notable for what I say next.
Chapter referenceChapter 1013Pre nerfed Kidd literally throws Big Mom down, damaging her with the force of her own weight. Similar strong attack also hurt Kaido prior.
Chapter referenceChapter 1031Kidd is stabbed by Killer, same guy who cut through Kaido with his blades and still takes hit from Big Mom
Chapter referenceChapter 1011Raw power of attack from Hera Kidd is hit with at close range
Chapter referenceChapter 1011Kidd takes little to no damage from BM's most powerful non fused homie from a direct hit.
Chapter referenceChapter 1030Kid tanks a Ikoku to the face and gets up to assign Big Mom right after with no issue
Chapter referenceChapter 1030The facct the armor is fully destroyed and Kidd is at the center of attack is further proof that Kid tanked it directly, or at least mostly.
The fact Kid can tank all of these attacks and still survive after being hit off guard by Shank's divine departure while unable to use haki to defend himself while charging up the rrailgun, is proof he is a durability monster. Not to the same exact degree as Big Mom or Kaido, but probably the closest tier underneath them. If that same guy was hit by Dorry and Broggy, do you really think that would be enough to kill him when the attack was focused on the ship rather than him directly?
Chapter referenceChapter 1079Kid is hit directly by Divine departure
Chapter referenceChapter 1079Kid and Killer confirmed to have survived the attack even if low durability
Chapter referenceChapter 1079Dorry and Broggy DO hit the ship, but not the crew members who could still carry kid and Killer to shore
I personally believe the member of his crew who is a fishman could have easily carried Kid away, and Heat is likely to have survived due to being the descednant of a Lunarian. It sounds wild, but in chapter 1024, he is shown to be able to breath fire.
Chapter referenceChapter 1024Heat breathes fire
This cannot be from an unknown devil fruit, as the heat fruit is in the possession of one of Big Mom's pirates, while Sabo is the holder of the Flame Flame fruit. It isn't a zoan or paramecia, as if it was a zoan Heat would be transformed and if it was a paramecia it would just be the heat fruit. As the flames come from his mouth, it cannot be strange technology as if he were a cyborg like say Franky it would not make sense. Despite Kid's technical knowledge that may rival Vegapunk's judging by the punk and 07 label on his rail gun, kid or adult Kid should not be capable of modifying Heat into a cyborg on his own. This is due t oa difference of materials as while Franky's scraps and metsl came from dvanced naval ships of enough quality to make an aincent weapon, Kid's island would have only literal scrap. His body is also not nearly bulky enough to be a cyborg and the marks on his skin are likely meant to show him patching himself together to ssurvive rather than metallic enhancements. Considering their island was unaffiliated with the world government, a Lunarian hiding and raising a descendant there is pretty likely, and could explain Heat's limited fire production, if so him having heightened durability due to this heritage makes a lot of sense. The SBS Oda talks about their bacstory is actually extrmely vague, and the fact we still do not know why Killer always wears a mask implies Oda plans on reveaing why soon, perhaps due to Killer being part of the three eyes tribe? If so, they would not need their ponygligh rubbings, as Killer already knows what they say
With these chain of events a logical issue is how would they survive even if they swam to shore? My answer to that is 1 for Shanks there would be no reason to chase the surviving crew members. Even if he saw them swimming away, their utter destruction is more than enough of a message of his strength, and he may not have seen it. After winning the fight, he probably went back to check on his fleet before going wherever he is headed, giant waves covering the remenants of Kid's fleet as they get the most important members to shore.
Chapter referenceChapter 1050Vagueness of the SBS on chapter 1050
Seriously, Oda would never make a backstory for a pirate as important as Kid this vague without expanding more on how Killer and Kid met, what Heat and Wire were like and are desended from when all four of the core Kid members seem to have special traits of rare bloodlines or clans, unless there was a reason for him not to do so. lf he knew he'd be making that an important part of the story or a movie later, this makes way more sense. Especially when this vague backstory has not explained why Kid is so clearly inspired from Rocks down to naming his Crew in the same mannner, wearing a similar robe come timeskip, and also these eerily similar expressions and visages unless they are something he will explain later.
The question for if they survived, is how Kid would even rebuild? My answer to that is Hawkins and X.Drake. In what seems to be Hawkins's final moments he laments betraying Kid and Killer in the first place, as shown here
Chapter referenceChapter 1052Hawkins given a 1% chance to live, just as high as somene like Kid survivng a wipeout from someone like Shanks
Chapter referenceChapter 1052Hawkins 'Dies' without us seeing the body when far more brutal deaths get shown directly
The fact Hawkins survived as long as he did after losing an arm, when him falling could simply be passing out actually makes sense. It's likely X Drake carried him off somewhere to be healed, and after Drake was seemingly betrayed by the government, both have nowhere to go, and could have wound up traveling to Elbaf, or gotten healed in Wano under fake identities and then traveled to Elbaf. Regardless, as Hawkins so desperately wants to join Kid but feels to ashamed to return, X.Drake could get him that medical attention and after learning what happened in the clash with Shanks, seized an opportunity. A chance to reunite with Kid and redeem himself for his prior treachery. My evidence for this theory? The very same card that was shown to Hawkins as Killer wiped him out as said by the narrator, the tower.
Chapter referenceChapter 1029The new way forward
The destruction of something old and brittle in this case, may not just be Killer cutting down Hawkins and the power weakening Kid, but the version of Hawkins who gave up before even putting up a fight. The weak man who wouldn't support another young pirate to try and make himself a Yonko of the sea as a result. Not to mention the version of Kid willing to fight an emperor without a plan or the power to back it up, a new way forward for both Hawkins and Kid simultaneously. After seeing Kid nearly died without him, what better time to apologize when his old partner has had his crew reduced (possibly from 31-16 or maybe even just the core 4 and some additional pieces) to show this time, he just wants to serve Kid with no strings attached, X Drake willing to join due to having no one else better to partner with for now. Even if Kid isn't quite Yonko level yet, with what he's already able to do plus how he'll likely emerge stronger, he should be far more powerful than Hawkins and X Drake anyway. Giving more reason for them to join.
Law is someone else who is likely to help Kid rebuild, as the nearest island would be Wano, and if he and Bepo arrived after X-Drake and Hawkins due to not having a ship or crew anymore, he'd be happy to join that alliance. His pride slighted by the loss to Blackbeard and BUGGY being chosen as an emperor over him, as well as Luffy who wasn't even an emperor of the sea officially due to the loss at Marineford. With no other options, joining a powerful and stacked alliance like that would be the best option, and he'd probably be okay with letting Kid take the helm as he'd be the only one capable of building anyone a ship. Even if he didn't want that, if they fought for the title a non-nerfed Kid would probably win that fight since he could take away Law's sword, and Law wouldn't be able to use most of his techniques effectively before getting hit into next year by a damned punk or one of Kid's other attacks. The only reason Kid did not try to use this against Shanks was he was bloodlusted and went for the ultimate attack instantly, this would not happen against Law.
While my earlier suggestion would solve the issue of raw strength/manpower for the Kid Crew, the question of the pirate ship does remain, as well as who would teach Kid Haki strong enough to be of help in the final war. Considering they would be in Elbaf, and Kid is known to take as he pleases, it's a very real possibility he removes wood from the Adam tree to build a far larger and stronger ship, naming it once more after Victoria due to the importance of her death. Who else would challenge him for this then Loki who has already stated he has no intention of joining Luffy? Likely because he admires Shanks. Considering the low chance for Shamrock to appear in Elbaf right now, and the fact we still do not know what makes Kid hate Shanks so much that he threw caution to the wind and tried to wipe him out with one big blast which is way different than how he fought Big Mom or Kaido, the two could bond over their shared hatred for Shanks, and how crazy Kid is. Keep in mind Shanks HAD to make a move against Kid's Damned Punk because he saw into the future way more than Kid could have predicted. When Loki sees Kid, and talks to the mad pirate briefly he would be the only person in the world capable of confirming Kid has truly inherited Rock's will, as he is the only pirate crazy enough to attack someone as powerful as Loki instantly just for questioning him. THAT would be enough for Loki to decide joining or at least showing Kid the basics of advanced Conqueror's, which would likely bloom similar to Roger's after a fight with someone as powerful as Loki, with an attack just like a cannon's.
As for why this ties into BAAD, think of the candidates the film could be about. It cannot be Imu or Joyboy, as even if it is non cannon they are far too important for Oda not to go into them at length in the manga/anime directly, even if the movie was not cannon, any spoilers for them would put the story at risk. So it cannot be about either of them without watering down their future reveals and tragedies and dimming down the speculation we generate by asking questions about them. It most likely will not be about Rocks as we will have just gotten a God's Valley movie two years ago. Does not make sense to have a canon movie about his most important day be followed by a non-canon backstory when Oda could just explore it in the anime/manga or in the 2+ hour long movie made to fill in the gaps left behind. The events have to be important enough to be interesting, while not so heavy for the overall themes of the story that they have to be resolved in story directly for it to be any good. Blackbeard is also unlikely because his full origin, revealing he scarred Shanks etc will likely be explained when it is finally his turn to have an arc, with the Rocky Port incident with Law having been so long ago everyone in it would look far too weak as those characters would all probably not have their most important power ups for them to agree to an alliance without killing each other.
For all of the events I just laid out, Kid getting a fully fleshed backstory, explaining how a Lunarian and a member of the ultra rare three eyed clan both landed on the same backwater island as a man from a long body? Tribe and Kid who is likely connected to Vega Punk while showcasing the 07 on his railgun + being the only person who may be the true inheritor of Rock's will, the only way to cover all of that in 2029, right as the final gears for the series should be turning and characters like Blackbeard, Dragon, and Akainu should be having their moments, would be a movie. A movie that could fully explain and flesh out Kid, the BAAD pirate who kills and pillages and after a crushing defeat wakes up to a strange wind chime, or possibly grew up with one. When Oda has already said he had an important role for Kid to play in mind since the start of the series, and the man he views as a rival in Shanks for likely wrong reaons due to the existence of Shamrock, Film BAAD is the best way to tie this all together. It gives time for all of these threads to get woven together without ruining the pacing of a future arc, and considering a backstoryless Kid got 31st of the popularity poll without any development, Oda knows the character is still relavant enough to warrant attention. Especially if he wants to give Luffy a true rival he can face in a fight that would not need to be to the death. It would also be funny given the only other person not named Luffy to get a movie for them was Shanks, the man Kid hates more than anyone.