In 2000, he pitched to the company the idea of creating a classic-styled fantasy RPG based from a tabletop RPG setting he made to play alongside his friends during his college days and gave to it the name Ar tonelico. However, the game was vetoed by Kazushige Masuda, who would later on be appointed as the director of the Atelier Iris subseries. Masuda told Tsuchiya that the game wouldn't garner much interest from the players due to the excessive focus it had on magic, as well as the extreme degree of difficulty it had because the spells depended on a complex synthesis system for their creation.
Therefore, Tsuchiya returned to his composer duties, though he also lent a hand by giving ideas such as the shop events and shop synthesis systems that were used in Atelier Iris: Eternal Mana, as well as also designing its logo and several other of its aspects. However, he still eagerly wished to make true his dream of making that RPG based on his own original world setting, and he saw his golden chance when Banpresto decided to approach Gust once again after having noticed how their first collaborative effort: Atelier Marie, Elie and Anise - Rumors of the Gentle Breeze, was a moderately successful game.
With this, Tsuchiya began maturing the idea for the game, and restructured the setting by making several large-scale changes to it, the greatest of them being the addition of the Reyvateil and Cosmosphere concepts. The latter one was completed with the collaboration of producer Atsunori Kawachi, who provided him with several tips, ideas and concepts gained from his experience on Banpresto, and it was through this clashing and harmonizing of ideas that Ar tonelico took its current form. He also was the main creator of the Hymmnos language used in said games, as well as its other versions, the New Testament of Pastalie, Carmena Foreluna and Ar Ciela. Aside of his work on the game setting and the games themselves, he was also quite attentive to the players and fans during the life time of the series, and served as one of its main PR outlets, being the creator of the Ar Portal official fansite, its Supporters' System and all of their related features, being one of the main writters and supervisor of the Toukousphere, and being the writter of pretty much all of the columns that appeared in the Ar Portal.