Being Mondo's older brother, Daiyaka's, "right-hand-man" in his biker gang, his younger brother basically trusts you with anything.

He promised he'd stick by your side ever since Daiyaka's death, and he always keeps his promises.

No matter what.

You could remember speaking to Mondo at Daiyaka's funeral, you could also remember the moment he made his very special and very unbreakable promise to you right next to his older brother's open casket.

He knew Daiyaka's death must've hit you like a punch to the gut, and he didn't want someone important to his brother to feel depressed. He wanted—no, he needed to stay by your side.

He wasn't obsessed, he was just protective.

Thus, promising to never leave you behind, he forced you to join Hope's Peak Academy as his right-hand-man.

You joined with your own special talent, and he joined with his.

Unfortunately for both of you, you two were walking mindlessly right in the face of danger and fatality itself.

Mondo knew it was his fault. He shouldn't have forced you to go. He should've just left you alone. He didn't have to make you join. It was entirely a choice..but he didn't want to leave you behind.