Responses
wasn’t sayoung the kid that J rescued before entering the rift? that means he was experimented on, artificially awakened to have poisonous powers, then rescued by J. they then bonded because J felt responsible for rescuing him. then J entered the rift and sa-young, who healed later on, then became obsessed with finding J

He's looking for YOU, Sa-young, ironically enough. Also, was Sa-young kidnapped by Prometheus AFTER J went into the rift? And he awakened while they experimented on him?