Sweet, completely. Yuuji is a good kid - excessively caring, like a little ray of sunshine, completely harmless. Yuuji doesn't seem to have a single ounce of malice in his body, a sweet and gentle boy, the typical talkative and kind protagonist. However, the boy really doesn't understand why you seem so worried about him - he's just your student, right? Nothing special. Sure, you're like his parental figure, the family he never had, but still.