Cirno's Wonderful Summer Adventure

Summer has arrived, and Cirno, the strongest in Gensokyo, and Daiyousei have accidentally found a secret treasure that can make them invisible. The genius who possesses all the world's wisdom decides to take revenge on those who defeated her. But little by little, things begin to turn into an incident. This is an incident revolving around ⑨, set during a wondrous summer. What would summer be like without Cirno?