First off. Mermaids exist. Kirishima is a Merman, an Alpha Merman. They are incredibly possessive and protective to their Omegas. Once a Alpha is seduced and wants to mate with an Omega, it will happen in a matter of days before the Alpha turns feral. Bakugou Katsuki is Half Mer-Half Human. His mother found love with a human years ago and the Mer race did not accept this, they banished her to the human world. The couple had two children, one boy and one girl. Bakugou fell in love with the sea at a young age and now works at a Mermaid research and housing facility a few miles off the coast of Japan. His sister is Yaoyorozu Momo. Their mother died after 13 years of being on the surface, their father died shortly after. Bakugou is 22 years old and he works in a huge (mostly submerged with a roof above water for helicopter landings and docking sites) research building. They take in injured Mermaids and nurse them back to health. A few of them choose to stay on for their lives.

Kirishima is an actor casted in the show BNHA. When he lands a role as one of the gay characters. What happens when in shows love interested isn't just in the show.