沉睡无数年头的福萨马格纳远古化石，因某个机缘合体复活，变成了和埃菲尔铁塔一样高的蜗牛怪兽。怪兽仿佛没有意识，只有本能，它缓慢滚动，整一路穿过东京到达大海。而它所滚动过的地方，都将变成废墟。日本的传统妖怪们惶恐不已，于是试图召唤天神渡辺纲的后代帮忙对付蜗牛怪兽。失去父亲的五年级少年渡辺兄（寺田心 饰）和母亲、弟弟相守度日。某个夜晚，他通过梦境见到了黑羽怪、辘轳首、雪女等妖怪。这些善良的妖怪请求渡辺兄拯救世界。考试还不及格的小男孩，又如何能成为救世主呢？ 灾难即将来临，妖怪大战争全面开启……
在有人神秘地将他的注意力吸引到了证据之后，一位无所畏惧的所得税官员袭击了勒克瑙最有权势的人的宅邸。
Gyeong-ah works as a caregiver and lives alone. The only one she can rely on is her daughter, Yeon-su, but it's hard to see her after she moved out on her own. Meanwhile, Yeon-su, who is suffering from her ex-boyfriend, Sang-hyun, argues with him again and visits her mother’s house. After Yeon-su left, Gyeong-ah receives a shocking message from a stranger.
