Responses
Tsubaki is pretty innocent, until that brat kid taught him what he read from her mother's novels/mangas works. The kid would stealthily read those works despite being not allowed as far as I remember lol. Unfortunately, the innocent genuine (no perverted thoughts) tsubaki got influenced by the brat.
How old is Tsubaki? If he is around 12 then I think is normal for him to have those kind of thoughts.
Now, if he is younger... That's different.