Toshiki Kumagai is a Japanese actor and voice actor born on September 18, 2007, in Kurashiki, Okayama Prefecture. He is affiliated with Avex Pictures. His career began in the performing arts at a young age, inspired by his older sister who studied musical theatre. He participated in the Kurashiki Music Festival at the age of six and began formal training after winning second prize in the singing category of the Kiratto Entertainment Challenge Contest 2016. He also received education at the Avex Artist Academy Tokyo School.

Before establishing himself in voice acting, Kumagai built a foundation as a child actor in musical theatre. He made his stage debut in January 2019 as Gustave in the Japanese production of Love Never Dies at Nissay Theatre. Later that same year, he appeared as a young Erik in the musical Phantom. His early voice acting work included the role of Keiji in the 2020 animated film Fushigi Dagashiya Zenitendō, a part specifically mentioned as an example of his work. He also voiced the character Ichirō in the 2021 animated series Yasuke.

His significant breakthrough in anime came in 2022 when he was cast as the lead character Yuhi Ohdo in the long-running franchise's series Yu-Gi-Oh! Go Rush!!. This role brought him wider recognition. In 2024, he starred as Hitoyoshi Yokoya in the anime series You Are Ms. Servant. His other notable anime roles from the same year include Raion Ōno in Tasūketsu: Fate of the Majority and Ryōta Kyōgoku in Himitsu no AiPri. He is also set to voice Takuto Ira in the 2025 anime Apocalypse Bringer Mynoghra.

In addition to original anime, Kumagai has an extensive portfolio in Japanese dubbing of foreign media. A pivotal role in this field was providing the Japanese voice for the young Simba in the 2019 Disney film The Lion King. He also voiced the titular protagonist in the Japanese dub of Remi, Nobody's Boy, Piak in The Letter for the King, and Josh in the Apple TV+ series Best Foot Forward. His work in video games includes voicing Sōji Kiyoya in 18TRIP and Yuhi Ohdo in Yu-Gi-Oh! Duel Links. In 2026, he is scheduled to voice Riliu in the anime adaptation of Suikoden.