The protagonist is Su Su Su, cosplaying as Speed Bullet Superman at a comic convention. Transmigrate? System, awesome! The world is ending? Saving the world is awesome!
Read the warnings at the very bottom.
Blurb:
A mechanical voice sounded: "Congratulations, Host. You have achieved the [Today I Finally Know Myself] milestone after 1,895 days."
"Open beginner's gift pack"
[Congratulations! You have obtained the skill Unlimited Learning Room and one clone. (This clone is an ordinary human.)]
I looked at the puppet in front of me, who looked exactly like me, and said, "From today onward, you are Brucie."
I left, taking the System with me. I left Gotham and set out on an unknown journey.
Bruce gazed at the manor from afar. Familiar scenes came into view one after another, as if he had returned to his carefree childhood.
He saw Brucie still living happily with Alfred at the manor.
…He had already made up his mind. He wasn't going back.
Clark Kent took one last look at the manor, engraving them firmly into his memory before turning away.
Warnings:
[I'm a complete beginner, just writing this for fun. I'm busy with work, so updates depend on whether I get the chance on weekends. It used to take me over an hour just to write a 600-word essay. I'm writing this because there's so little to read, and nobody else is writing it, so I'm making my own questionable meal. There will be some OOC, a lot of OOC. I haven't read the official material, so this is all adapted from fanfic plots. Also, I'm a fan of bad endings. I like beautiful but tragic characters, and I have some nasty tastes. For example, I'll work in cruel tropes I've seen before, like being left completely alone, everyone dying, or leaving decisions up to a wheel spin. Anyway, if you see it, don't curse me out. If people do, I'll really abandon the story. In short, don't curse me out. Go yell at the official DC writers instead, thanks!]
Theme: Saving the world, saving yourself