Kōki Koyasu is a Japanese voice actor known for his work in several anime series. He is the son of the renowned veteran voice actor Takehito Koyasu, and the two have appeared together in at least one production. His career includes both supporting and minor roles across a range of fantasy and comedy anime titles.

One of Kōki Koyasu's notable roles is Curtis in the fantasy series The Banished Former Hero Lives as He Pleases. In this story, the main character Allen is banished from his noble family for being deemed weak, hiding the secret that he was a great hero in a past life. Koyasu voices Curtis, who is identified as the younger brother of the character Anriette. His father, Takehito Koyasu, also appears in the same series as the character Craig, Allen's father.

Another significant role for Kōki Koyasu is Hank Beat in the anime Kunon the Sorcerer Can See. Hank Beat is a character who appears from episode eight of the series, which premiered in early 2026. The show follows a blind young man named Kunon who uses water magic in an ambitious attempt to create new eyes for himself.

Beyond these two primary roles, Kōki Koyasu has a few other confirmed credits. He played the part of Researcher C in the second season of the romantic comedy series The 100 Girlfriends Who Really, Really, Really, Really, Really Love You. He also voiced the character Roy the Burning Pen in the series Arad Senki.