for fantasy au i love the idea that all of izuku’s human friends freak out at the thought that katsuki has izuku’s initial straight up tattooed on his arm?
but izuku loves it; he knows it’s a custom of their people. because while humans form bonds that are paper thin,

the dragon tribes have rituals that bond souls—so they’re not afraid to mark their skin, because they’re not afraid that something trivial will pull their bonds apart.
“what if you guys have a fight and break up?!”
it’s easier for izuku to just shrug it off than try to explain.

katsuki, though... he tends to fly into a rage when he hears some human insinuate that izuku and him can be pulled apart by words.
ochako asked izuku once, if that was true, why he didn’t also have a tattoo?
“it’s not his tradition.” katsuki butted in.

“deku isn’t expected to follow the ways of my people if he doesn’t want to.”
“mitsuki-san told me to think hard about it before i agreed, because it’s unusual as far as human customs go.” izuku continued. “but... i have been mulling it over... and i think it’s something i want.”

ochako had never seen such a blinding grin from katsuki before that moment, nor since.
his friends don’t hear anything about it actually happening though. it’s not until they’re all forced into a war to save the kingdom that they end up seeing it.

izuku’s sleeves are in tatters, exposing the stark black K that sits on the opposite shoulder to katsuki’s.
“you finally did it!” ochako comments, though only once the actual threat had been neutralized. “wow... it kinda feels like you’ve always had his initial tattooed on you.”

“i have,” izuku smiles. “it just hasn’t always been written so plainly on my skin.”
“hm?” her head tilts a bit, questioning.
izuku looks for him in the distance and puts his hands against his chest. “his name’s been tattooed on my heart for as long as i can remember.”