Twelve year old Sei has hit puberty and is quickly becoming sexually aware, sometimes not as privately as he'd like; erections in school and other inopportune times plague him. He talks about it with his school friends, Kinta and Nyanko, in between their feuding over the affections of classmate Yumi, but can't figure out what to do about it.

某个平静的早晨，久保家的顶梁柱毫无征兆地离开人世，只留下妻子房子（松坂慶子 饰）和三个儿子相依为命。在此之后，奔丧而来的叔父（岸部一徳 饰）和他们住在一起，组成一个新的家庭。为了养活孩子，房子身兼数职，辛苦打工，偏偏孩子们还性格各异，问题多多。沉稳老成的长子政司（久野雅弘 饰）恋上了美丽的女大学生由加（加藤夏希 饰），对方却有着恋父情结；次子行雄（森田直幸 饰）是个直来直去的莽撞少年，某天他发现和父母兄弟长相不同，因此开始怀疑自己的身世；幼子宏基（大塚智哉 饰）正就读小学，心中时时刻刻希望变成女孩子。久保家的故事在大阪的天空下缓缓展开…… 本片根据森下裕美的同名漫画改编。