When he was young, Mitsuzane was raised by his older brother, Takatora Kureshima, as his parents spent most of their time overseas.
Mitsuzane later became a member of Team Gaim in his teenage years, becoming Armored Rider Ryugen and competing alongside Armored Rider Gaim in the Inves Games. The team quickly ascends to the top of the rankings, allowing Mitsuzane to discover the conspiracy revolving around Helheim Forest and the Inves. However, after realizing that Yggdrasill framed the Beat Rider Teams for the Helheim conspiracy, Mitsuzane discards his Sengoku Driver. He reclaims it when Kouta and Kaito are captured by Yggdrasill and uses it to save them.
At the same time, Mitsuzane unintentionally reveals to Takatora on camera that he is an Armored Rider, causing Takatora to confront Mitsuzane. Takatora confesses the truth about Helheim. Mitsuzane decides not to tell his friends, which leads to him to betraying them several times.
After Ryoma's group ousts Takatora, Mitsuzane takes his Genesis Driver, allowing him to become New Generation Rider Zangetsu Shin. Mitsuzane begins to blame Kouta for all of his hardships and, after Takatora allies with Kouta, he uses Zangetsu Shin to attack Kouta in order to break up their alliance. Though this fails, Mitsuzane allies himselfs once Project Ark fails and becomes more sadistic as everyone continues to protect Kouta.
After the failure of Project Ark, Micchy allies himself with the Overlord Inves, assisting Redyue in her plans. When he discovers that Takatora is still alive, Mitsuzane attacks and seemingly kills his brother, as well as permanently destroying his Sengoku Driver.
Mitsuzane later learns that Rosyuo is dead and that Mai is the current bearer of the Forbidden Fruit. This causes him to ally with Ryoma and is sent by him to kill Kouta. When he returns, having succeeded, he finds that Ryoma vivissected Mai to recover the Forbidden Fruit. Realizing that everything he accomplished nothing but apparently kill his friends, he breaks down, but is comforted by Takatora after he returns.
In the aftermath of the Helheim invasion, Mitsuzane becomes the last person wielding a Sengoku Driver and becomes a hero once again.