Ageku no Hate no Kanon  

And he arrived at the Kanon., あげくの果てのカノン, And He Arrived at the Kanon

In this scenario, there is an alien invasion that forced most humans to live underground. However, in a town where it constantly rains, a young girl named Kanon Kouzuki is focused on other matters. As one of the few people living aboveground, she is reunited with her former crush Sousuke Sakai, who is now a famous alien fighter. Kanon is now fixated on Sousuke and begins to observe him more closely. Will he be the same boy she fell in love with before or will he have completely changed?