Mitsumi is a small youkai who appears in the first segment of the 2021 film Natsume's Book of Friends: The Stone Waker and the Strange Visitor. This character is encountered by Takashi Natsume in a forest while Natsume is searching for Nyanko-sensei. Mitsumi serves as a subordinate to Gantetsu, a powerful and divine water spirit or ayakashi, and has been entrusted with the role of Ishi Okoshi, or Stone Waker. This role involves waking Gantetsu from a deep slumber using a designated ritual or method. Mitsumi is eager to fulfill this duty as a way to prove worth as a servant to Gantetsu and to repay a debt of kindness. The character is depicted as meek, small in stature, and sincere in demeanor, which earns Natsume's sympathy and trust. Noticing Mitsumi's earnest desire to succeed and the difficulty of the task, Natsume decides to help. The situation is complicated by the fact that other youkai, including Nyanko-sensei, seek to take over the waking role for themselves because Gantetsu rewards whoever awakens him with sake. This creates a light-hearted competition that puts pressure on Mitsumi. Throughout the first story, Mitsumi remains determined despite the obstacles. The key relationship is with Natsume, who acts as a protector and supporter. Mitsumi also has a subordinate connection to Gantetsu, whose favor is the goal of the mission. The character does not display overt combat abilities; the notable trait is the assigned ritual responsibility rather than personal power. Character development is minimal but present: Mitsumi begins as a nervous youkai struggling with an important assignment and, with Natsume's aid, gains the confidence and opportunity to see the task through to completion.