One day, five kindergarten children suddenly disappear from a kindergarten in Tokyo, sending their teachers and parents into a panic. The five of them are connecting on trains and headed to an unfamiliar place for some purpose. Before their journey, they had made a promise to each other “not to cry no matter what happens”

高木护（阿部真夫 饰）是一家文具公司售后部的职员。一天，在同学聚会上遇上了多年未见的棒球部好友世仓纯一郎（葛山信吾 饰），交谈中得知他离婚后独自带着双胞胎笹仓薰（芦田爱菜 饰）和笹仓友树（铃木福 饰）生活着，护回想自己到现在连个女朋友都没有，心生感慨。翌日，护和同事拜访客户后回到公司，接到了纯一郎的电话，但看到自己暗恋对象牧村加奈（泷泽沙织 饰）就挂断了。几天后，他接到了棒球部同学的电话，请他去参加纯一郎的葬礼，原来纯一郎得了癌症，却一直没告诉亲友。护在火葬场听到纯一郎的家人讨论双胞胎的去处问题，协商结果是让他们分别去两个家庭生活。数日后友树突然丢了，护接到消息一起帮忙找他，与此同时，因为迷路哭泣的友树遇到了一条会说话的狗Muku。护几经找寻，总算找到了人，想起纯一郎生前曾说过孩子们觉得一直在一起才是最幸福的，护决定先暂住他家一星期，高木护、世仓薰、世仓友树和Muku开始了同居生活……

Daikichi learns that his recently deceased grandfather has an illegitimate daughter with an unknown mother. The girl's name is Rin and she is just 6 years old. Everybody in Daikichi's family looks at the girl as an embarrassment and wants no part of her. Daikichi, annoyed by his family's attitude, decides to raise Rin by himself. Even though Daikichi himself has no experience raising a child and is still single.