Often loitered around on the street.
His first appearance was in the initial chapter of the series, "Slow Awakening", chucking up his stomach's content due to his sea sickness.
After their arrival on Cat Island, Semimaru tested out his companions' personalities right away by bullying and challenging them, going as far as attacking Botan with a knife and sexually harassing her because he didn't buy her feigned innocence. Her cool response discouraged him and made him step back though. When Arashi and Natsu ran away, he decided to stay with Botan because he trusted at least in her survival skills. Reunited with the rest of the team later on, he travelled together with them to Fuji.
After the group split up there, Semimaru followed Arashi and Natsu to [Southern Honshu]] because he wanted to find out what had happened to his home town, Hamamatsu. When he realized there was nothing at all left, he didn't waste much time on grieving, but only set up a grave stone and after a silent talk with his deceased mother, decided to move on in order to survive.
Together with Natsu, Semimaru supported Arashi when he fell into despair and travelled back towards Bungo Fuji with them. When they picked up Hibari along the way, he strongly disliked her bullying Natsu because he declared her as "his prey". He also scolded Natsu for hiding the letter, but praised her "newlyfound depth of character" and covered for her in order to hide her secret from Arashi.
Later on, they came across Ango and Ryou. Semimaru judged them correctly as "kids from a sports camp way out in the boonies" but was a bit wary when he discovered Ryou's abilities with a knife. His attitude quickly changed to admiration especially for Ryou though due to his vast knowledge and honed skills. Semimaru at some point even went as far as calling him "sensei".