故事始于2046年，为了追捕侵袭火星的外星人多鲁米斯星人，宇宙探索舰Lysithea号在各地挑选先发人员，初中生美加子也成为一名宇宙员。开始了辗转于火星、太空基地、木星、冥王星等各地的演习。美加子离开地球后，她的同班同学小昇仍然能收到来自宇宙的问候——美加子时常发来短信告知近况，只是随着距离的扩大，短信送达地球的时间就会越来越长。“有一天一定能再见面吧！”对方都这么想着。可是，美加子终于杳无音信了。 8年后小昇的收到这样的短信“24岁的小昇你好，我是15岁的美加子哦！……”

This book focuses on a juvenile to tell three continuous stories Cherry Blossoms, Astronaut and Five Centimeters per Second, which compose together forming a complete book. This is a story that quietly and slowly enters into your heart. It describes the change and non-change of love, as well as the wander of soul. The world is so beautiful, and the youth is so gorgeous, but the hero of the story is only willing to talk to himself. ""What is the furthest distance in the world""? For the youth who is always living in yesterday, walking out of his inner world, is the most long distance...The story is simple but very real, and can stimulate the silent touch in the deepest corner of heart.