My idea is that a person gains the ability of the Nodos from the anime Heroic Age so our character can turn into the Bellcross and the other heroic tribe members that are shown in the anime or at least just Bellcross ideas for fanfics for this could be other space related animes like Gundam, Robotech Macross series, the Mass Effect games, pretty much anything that has mechs in them, could also use Attack on Titan, and so the character can fit in other worlds like a fantasy world like Danmachi, or worlds like Marvel and DC maybe have the main chapter have two forms, the full 15 meters Bellcross form as well as a smaller perhaps Bellcross themed armored form or something same thing for the other Heroic Tribe forms if you add them in. If we go multiverse if you have the mc have all the Heroic tribe in the story maybe you can use what the anime did at the end in which the Nodos Kerbius and Bellcross form that portal mirror that supposedly leads to where the Golden Tribe went, and so the mc isn't straight up op from the start have him have to unlock the other Nodos and then when he unlocks Kerbius then he can travel the multiverse.