In 2005, a capital and business alliance between Toyota and Subaru was announced. In 2007, the two companies began to deepen their relationship in many areas, including production and development, with Subaru commencing contract manufacturing of the Toyota Camry sedan on its US plant production line. The Subaru Tresia is the result of this deepening relationship between the two companies. Although the Tresia was developed on an OEM basis from the Toyota Lactis (2nd generation P120), which was based on the Toyota Vitz, its development was carried out by engineers from both Toyota and Subaru, with over 100 Subaru engineers participating in the development of the Lactis. As a result, the DNA of Subaru's car-making process was strongly reflected in the RACTIS and TREZIA, resulting in a car with a different ride quality from previous B-segment Toyota cars. The word 'Tresia' was coined from the English word 'Treasure', meaning 'treasure'.

Otonokizaka Gakuin, a traditional school located between Akihabara, Kanda and Jimbocho, is on the verge of consolidation. Nine girls, led by second-year student Kosaka Honoka, rise up to meet the school's crisis. What we can do to protect our favourite school. ...... That is to become an idol! Become an idol to publicise the school to the world and increase enrolments! This is where the girls' 'story of making it happen together' School Idol Project began!

In charge of music production in μ's. First-year student at Otonokizaka Academy. The only daughter of a wealthy family whose parents run a large hospital. She is hard-working and proud, but at the same time she is not good at communicating with others. She had aspirations to become a musician, including writing her own songs, but her parents expected her to take over the hospital as a doctor, and she almost gave up on her dream of becoming a musician. At that time, she was approached by Honoka Kousaka, the founder of the school idol group μ's, to write music for μ's and join as a member of μ's. After some hesitation, she agreed and became a member of μ's. She then pursued her dream of becoming a musician once more.