[Crossover] I'm the Big Brother Across the Heavens

[Revising at a snail's pace] The superhero who holds back tears and pain, strong and unyielding; the emperor of the seas who commands an entire realm; the Superman who soars through the heavens and dives into the earth; the hero who embodies fear; the flash from the land where leaves burn. They are the embodiment of strength. But in front of you, they don't hide their vulnerability. Whether you are frail and helpless or possess the might of a demon god and the terror of hell, to them, you are the one who protects them. They will depend on you. They will call you... Big Brother. No matter how powerful and fearsome they become, no matter how strong, unyielding, or brilliant they are, Everyone seeks their protection or wants to take their place. They are praised or feared. But he was once someone protected by his big brother, too. A domineering, protective big brother who's also a little chuunibyou. Contains original headcanons. Please forgive any OOC. Premise: A dependable and handsome big brother!