Semimaru was very calm and did not show much of a reaction in crisis, such as when Oden attacked Orochi, as he simply put up a barrier to protect the latter. When he saw Oden humiliate himself on the street of the Flower Capital, he cackled with his family members, enjoying their successes.
Semimaru was loyal to his family, and went along with Higurashi plot to make Orochi the shogun. He was seen laughing with them in triumph after they had forced Kozuki Oden, their rival to the shogunate, to humiliate himself.
Semimaru ate the Bari Bari no Mi, a Paramecia-type Devil Fruit that allows him to create barriers at will. With this ability, he was able to easily shield Orochi from attacks with an unbreakable barrier.
Twenty-five years ago, Semimaru was with Orochi and Higurashi when Oden returned and attacked Orochi, and he created a barrier to protect Orochi, rendering Oden unable to remove him from power. 20 years ago, Semimaru accompanied Orochi and Higurashi to Kuri as Orochi told Oden of his intention to build factories there.
Semimaru eventually died of unknown causes, as his fruit is currently in the consumption of Bartolomeo.