Doraemon and Nobita are having a usual quiet day walking on the street until they hear Gian practicing for his concert from the Open Lot. While Nobita suggests them to take other route, Doraemon instead persuades him to just rush across the lot while shutting off their eyes and ears, which unfortunately leads them to become the audience for Gian's practice. As they listen to the atrocity, Nobita wonders why Gian is unaffected by his own song, which Doraemon tactically replies that "a pufferfish is immune to its own poison". Fortunately, a man appears to stop the practice and instead persuade Gian to record his song for him. After the man has left, Gian reveals to the two that the man is in fact a vice-principal to the famous Grand Prix Music School, and he has come to scout him to be the new star, leaving the two flabbergasted by the event.
After Shizuka and Suneo are told about what has transpired, the latter concocts a theory behind this strange event: the Perfect Murder Case. The murder would be carried out by the vice-principal by having the principal's listens to the recorded song every night. Though there might be no effect at first, the culminating poisonous song will eventually take his life and the vice-principal can easily take over the school with the police being none the wiser due to lack of evidence. Suneo names this "Gian Murder Case", terrifying Nobita, Doraemon, and Shizuka, though Suneo quickly changes the topic once Gian appears with his "Weight-Reducing Paint Roller" to prepare to become a star.
Still worrying about Suneo's theory, Doraemon and Nobita use "Police Dog Nose" to find the location of Grand Prix Music School, discovering that the school is in fact in a dire financial and reputational problem. Using the "Invincible Mantle", the two sneak inside the building and listen to the vice-principal and the principal's conversation. Much to their relief, the vice-principal and the principal are actually planning to use Gian's singing voice to advertise their school by having another boy with similar voice (but better at singing) to perform and advertise these as singing "before and after" entering their school. Though glad that there is no murder case, Doraemon and Nobita are left wondering whether to tell Gian about the fact that he won't become a star anytime soon.
- Nobi Nobita
- Takeshi Gouda
- Shizuka Minamoto
- Suneo Honekawa
- Vice-Principal of Grand Prix Music School
- Principal of Grand Prix Music School