Well I just updated it so if you download it again, the main missions and closet reward will give you enough money to buy the art.
Found the bug, if you decide not to continue the fight against Susamaru and instead you get to Amane's mansion when you get back the game will skip from the mission against Kanao, Muu and Zeniko to the mission against Rui's familly which requires that you talk to Shinobu but you cant without getting Kanao.