Mari Sonoda is a member of the Ryusei School entrusted with guarding the Faiz Belt and one of the main protagonists of Kamen Rider 555.
Mari was one of the orphans taken in and raised in the Ryusei School by Smart Brain's former chief Hanagata. As an adult, she was sent the Faiz Belt and Auto Vajin by Hanagata, leading Smart Brain to send Orphnoch assassins to pursue her. Mari initially attempted to use the belt herself to fight back but was unable. However, in a chance encounter with Takumi Inui, Mari placed the belt on him and discovered he could use it. Takumi became Faiz and fended off the Stingfish Orphnoch sent to retrieve the belt.
Mari generally believes in the good of her friends, which makes it easy for those like Masato Kusaka to hide their true natures from her. She seems to be oblivious to the affections of others as she failed to notice Masato and Sawada's crushes on her since childhood. She often teases Takumi for being a "nekojita" though she greatly cares for him.
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Super-1
Kamen Rider ZX
Kamen Rider Black/RX
Kamen Rider Kuuga