. Hikaru became addicted to drugs when he was nine years old. That was during an incident where he was tied down to a chair. It was the same incident as the spider incident, just on a different day. He was drugged, then given time to get off the high, and was drugged over, and over, and over again until he nearly died.

. After that incident, he'd become pretty addicted to drugs, especially a highly addictive one called tosui (a made up drug that I came up with for the My Hero Academia universe). It heals physical wounds, but it can be dangerous mentally and, when abused, causes damage to the organs. It's highly addictive which is why it was made illegal.

. Tosui makes him euphoric, so he often is much more smiley and giggly on it. He doesn't typically chuckle or giggle, especially giggle. So that's one way to tell that something is up.

. When he's high, he stumbles more and is much more clumsy than he usually is.

. By the time his high has worn off, he gets extremely drowsy and ends up falling asleep. Then, when he wakes up, he feels groggy— and he sometimes feels depressed.

. By the time he wakes up when his high wears off, he'll also feel pretty hungry.

. He sleeps so soundly when his high wears off that he will pee in his sleep.

. When he knows that something he's doing is wrong, or the way he feels about someone or something is wrong, yet he doesn't want to change his mind, he argues with himself. Sometimes out loud, but usually in his head. Sometimes he creates an illusion to argue with.

. Despite naturally being a thinking type, it can be hard for him to not get caught up in emotions.

. When he's being guilt tripped, he is sometimes aware of it, and he can fall for guilt trips, too. He tries not to, but he just feels so... guilty.