From Anime News Network:

This is a two-part manga that was printed with three other short stories together in one book. The tankoubon itself shares the title of this story, Firecracker is Melancholy.

Story 1) Kanshakudama no Yuutsu: Kajika is a female ninja and her parents were murdered by the rival ninja family Hayato when she was a little girl. Now, she lives with her grandfather. She falls in love with her senpai named Fujisaki. But he thinks that Kajika is too male. And Kajika's childhood friend Yuga has a problem with Fujisaki-senpai! When Fujisaki wants to date Kajika, she discovers something that is really shocking and surprising for her...

Story 2) Kanshakudama no Yuutsu-Kimi ga inakucha (without You): Yuga can't go home with Kajika because he has some meetings with the SMV. He goes to the meetings with Fujisaki-san, the sister of Fujisaki-senpai, who fell in love with Kajika because she gave him freedom and mercy. Kajika is sad because she thinks that Yuga loves Fujiya-san, but she doesn't know why. Yuga challenges Fujisaki-senpai because of Kajika. But Yuga isn't a ninja, that's why he asks Kajika's grandfather for training. But Kajika is getting more sad because she thinks that they want to fight because of Fujiya-san...

Story 3) Kono Koi ha NON Fiction (This Love's Non-fiction): Yuri wants her best friend Karin, a rich girl, to meet her pen friend because she sent him a photo of Karin. For an ordinary dessert (a cheesecake) Karin do that, and she has a date with Ryo in the aquarium, but nothing is like it should be - appearances are deceptive...

Story 4) Ame no Gogo ha Romance no Heroin (Rainy afternooons are for romantic heriones): Minori falls in love with Takato-kun, a boy from an other school because one day he gave her his umbrella when it was raining. Since this day, Minori hopes that there is rain all the time because she wants to be with Takato under his umbrella. But in the middle school Takato got a go-by of a girl and there is a rumour that he hates all girls since this day. What will Minori do and WHO was that girl...!?

Story 5: Ni Banme No Koi No Katara (The style of a Second Love): This is Tanemura Arinas debut in the year 1995 or 1996. Mana loves the boyfriend of her bestfriend Yume. But the most popular boy at school, Nakamura Shigenobu, loves Mana and he doesn't give up. But Mana doesn't want to fell in love with someone else until she forget Nishikawa.kun, the boyfriend of Yume.