Ieji Hisashi was involved in an explosion that occurred in a town during a job assignment away from his family, but miraculously returns to life from a 3-month coma. However, he is told by the brain surgeon, Tsukuba Yoshiaki, that he is suffering from higher cerebral dysfunction due to the effects of the accident and has a fuzzy memory of the recent five years. He used to have a glamorous life as a sales representative for a securities company, but the damage to his brain has also affected his work. He is transferred to the unimportant Thirteenth Sales Department from the star department, the First Sales Department. Hisashi has to live a corporate life that is a stark contrast to the past. The only things he has left are dim recollections and a mysterious bunch of 10 keys. Even so, I have my dear family, he tells himself. He unlocks the door and steps into an empty house in a quiet residential neighbourhood. It suddenly starts to rain. He hurriedly takes in the laundry and when he is ironing the clothes, his daughter, Subaru, and ex-wife Kaoru, return. They are alarmed that he is here. This is the house where Kaoru, whom Hisashi divorced five years ago, and Subaru live. It is not Hisashis home any more. Because of his fuzzy memory and forgetfulness, Hisashi writes down things that occur daily in a diary as he tries to retrieve the past little by little. However, he is occasionally under illusion that his routine more than five years ago is the existing reality. This time, he ended up coming back home to Kaoru and Subaru. He hastily hands back the key and heads for the house he should return to where his current family waits. It is an ordinary home where he lives with his wife, Megumi, and their 4-year-old son Yoshio. However, Hisashi sees the faces of Megumi and Yoshio as masks. He can neither tell their facial expressions nor their emotions, let alone his love for them. This distresses him. On the other hand, he feels love for Kaoru and Subaru. What sort of days did he have in those five years which are a blank to him? Hisashi decides to set out on a journey to find his past self, relying on the bunch of keys that he has. He becomes aware that he was a cold, career-minded man before the accident while he visits people connected with his past. The persona that is gradually revealed is beyond the imagination of his present kindhearted self.
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