Today is the fun, once-a-year Christmas concert! Dokin-chan, disguised, is practicing a song with Shokupanman and the others. When Kokin-chan sees this, she says, "I want to sing with you too!", but Dokin-chan just says, "No!". Kokin-chan becomes sad and starts crying as she usually does, but for some reason she seems different than usual. At first Dokin-chan was angry, but then she becomes worried and goes to look for Kokin-chan, who has run out...

(Source: Amazon, translated)