Vice-Captain of the Defense Force's Third Unit. A member of the Hoshina clan, a family of Kaiju exterminators dating back to the Muromachi period, and the younger brother of Hoshina Soichiro, Captain of the Sixth Unit in the Western Division. In the Defense Force, which primarily uses long-range weapons, he uses swords as his main weapon because his released power with sniping weapons is low. In combat, he utilizes Hoshina-style Extermination Arts. While he falls behind Ashiro Mina in dealing with giant Kaiju, he is superior in exterminating medium and small-sized Kaiju, possessing enough combat power to fight on par with the Daikaiju, Kaiju No. 10. His reinforced suit release rate was 92% at the beginning of the story—the third highest—showing incredible speed that is described as being beyond human movement. His personality is generally relaxed, cheerful, and a bit mischievous, but he becomes extremely serious during missions. Although he won't admit it himself, he has a bit of a battle-maniac streak. He speaks with a Kansai dialect, as he is from that region.

A suit created based on the remaining parts of Kaiju No. 10 after it volunteered to be weaponized, referred to as Numbers 10. It is the first Kaiju weapon in Defense Force history to possess its own will, characterized by No. 10's eye in the cross-shaped hole on the chest and a long, sharp tail. Because it has a will of its own, it cannot demonstrate its full potential if it does not agree with the user. Conversely, if their opinions align, it is a suit capable of pulling out combat abilities beyond the original capacity of its compatible user, Hoshina Soshiro. Kaiju No. 10 has control over the tail and uses it to express its intentions. However, if Soshiro loses consciousness, control over the body may shift to Kaiju No. 10.