|Weapons||Twin Colt M1911 pistols|
|Japanese Voice||Chise Nakamura|
|English Voice||Cherami Leigh|
Itsuki is first introduced in chapter 16 of the manga when Takamasa got granted the rank of Gon Sojo by the Kōgon Sect through promotion. In the past, she died in an automobile accident and came back with the regret of not living a life of a normal teenage girl. She bonded with Takamasa because she thought he was a powerful monk and would quickly help her get to Heaven. Unfortunately, Takamasa knew nothing about the Shikabane Himes before that. Regardless, they both continued to work as a team. During their time, they began to develop romantic feelings for each other. However, they were unable to act on them because Itsuki is a Shikabane Hime.
In the anime adaptation, Itsuki first appeared in episode 5 when she enters Ouri's high school as a transfer student along with Takamasa, who initially appears as the school's nurse. Later in the episode, Itsuki and Takamasa would finally reveal themselves working for the Kōgon Sect when they were confronting the traitor monk, Akasha Shishidou while rescuing Ouri. She was also a former friend of Tomoharu Kishibe who became a Shikabane after he died in a car accident with his family when a group of teenage drivers made them fall off the cliff. Four years later, Itsuki and Takamasa would finally kill him near the end of episode 4 of season two.
- The name Itsuki means "different, singularity, queerness" (異) (i) and "moon" (月) (tsuki), which literally means "different month" altogether.
- Itsuki's surname Yamagami means "mountain, hill" (山) (yama) and "god" (神) (kami/gami).
- Itsuki has Type O Blood.
- Itsuki's height is 154cm and her weight is 44kg.
- Itsuki's mental age is 18 (physically 16).
- Itsuki's birthday is March 18th.
- Itsuki's favorite foods are ice cream (preferably Vanilla), xagen dax, pasta and pizza.
- Itsuki's least favorite food is anything spicy (curry is an exception).
- Itsuki's specialty is artistic gymnastics.