Semimaru has a crush on Natsu. It was one-sided throughout most of the series (as Natsu liked Arashi), but it’s heavily implied Natsu likes him back, seeing that she got jealous over Semimaru complimenting Hana. Semimaru and Natsu have kissed twice.
His mother was a night worker, as a result, the parents of his peers often gossiped about his family, leading to Semimaru being bullied as a child. His mother hardly ever cooked, but once in a while, she would make him delicious stew.
Semimaru doesn't know his real father because his mother refused to divulge any information regarding his father.