Celebrating Christmas for the first time as a member of society.Onmura Yuki (played by Kiyohara Goya) lives a busy and fulfilling day as a new teacher. Wada Toranosuke (played by Mochizuki Ayumu) ​​asked her if she had any excuses to meet 5 people, and told her how longTanigawa Airi (Mikami Ai) is going back to Tokyo.Yuki felt lonely that the five people who had spent the same time together not long ago had fallen apart like this. She accidentally saw the words "Christmas “present”" and Yuki began to reread her life diary...

Two months ago.The paper written by Hiroyuki Tokunaga (Yuto Sano) won the prize given to young researchers.The relationship between Yuxi and Guanghai is also going very smoothly, but for some reason, Yuxi feels uneasy that everything will collapse because of one thing.

At this time, Yuxi attended the award ceremony with a gift for Guanghai.After the ceremony, Yuki went to Guanghai's side, but before that, a strange woman spoke to Guanghai.That was Guanghai's acquaintance in the United States, Chu Feng.Feng handed a piece of paper to Guanghai as a congratulatory gift.On it were written math problems that Feng had done himself.The unique feeling of intimacy between companions walking on the same road made Yuki feel timid.Moreover, during the conversation with Feng, I learned that Guanghai rejected the invitation from American University...

Later, after graduation, under the name Guanghai's celebration, the five of them got together for the first time...