Natsu e no Tobira  

Door to Summer, Natsu he no Tobira, Opening to Summer, The Door Into Summer, 夏への扉

Marion is a schoolboy who follows a philosophy called "rationalism." he values logic and reason over emotions. however, when he gets involved in a romantic relationship with an older courtesan, his rational approach is exposed as just a way to hide his emotional immaturity. through her care, marion learns how to love but unfortunately, he hasn't yet realized the true cost of this affair.