En has been good friends with Atsushi since their middle school years. Their first proper meeting was the time En prevented Atsushi from tripping over on his way to Kokokara Curry by grabbing his wrist as support.
They both then realised they were heading towards the same destination and decided to go there together. En and Atsushi’s similar interests are what helped develop the relationship they maintain as of now, and what also teared the friendship of Atsushi and Kinshiro apart. Their friendship became stronger as Kinshiro began distancing himself from Atsushi.
Despite their personalities being the complete opposite; with En being the laid back and self-paced person and Atsushi being the serious and hard-working, they are very close friends and are often referred to as a ‘married couple’ in various official resources such as the light novel and magazine. Atsushi is often referred to as En’s ‘wife’ and the motherly figure of the defence club. En once stated that the latter gives off a scent of a good wife and a wise mother, while also having a manly feel simultaneously. Whenever Atsushi isn’t present by his side, there can be a sense of emptiness felt through his words. For example in one of En’s monologue in the light novel, he states ‘The Atsushi who’s always by my side, isn’t here with me today’.
En also refers to Atsushi as being an air-like presence to him in different official resources such as the anime, otome game and character interviews. In episode 9 ‘Love is stronger than pride’, En first states that Atsushi is like air to him which the latter is confused as of whether to take his words as a compliment or an insult. In En’s character interview in the Boueibu Mook, En states that whenever the two hang out together, rather than having the feeling of being together, Atsushi plays En’s games or watches DVDs as he wants while En does his separate activities such as reading manga or idling around in the background. He then refers this relationship he has with Atsushi as ‘air’ again. Also, in the Yufuin En’s Monologue side route of the official otome game, En finally clears the meaning of Atsushi being like air to him. Despite the pronouns used in this monologue remaining ambiguous (therefore is not cleared whether En is talking about the
protagonist or Atsushi), it is obvious by En’s descriptions of the person that relate back to the previous side routes when the two are spending time together alone without the protagonist that En is suggesting Atsushi. En, conflicted over his feelings towards Atsushi after being interrogated by Io in the infirmary room, states that something like love is bothersome for an individual like him to begin with. He then continues by saying that his feeling towards the latter and the latter’s presence is like oxygen, or in other words something he cannot live without. This strongly suggests his feelings for Atsushi as well as how important he is to him.
In their free time, usually after school, the two usually visit a park or a café to sit and chatter about self-centred things. Whereas in the weekend, Atsushi often has to come to En’s house before the planned time of their meeting to wake him up and do the preparations for him such as choosing his clothes, making breakfast, etc.
At one point, En even stated that he stored romantic feelings towards Atsushi. In the otome game universe, if the player obtains the ‘friendship end’ after failing to get the ‘love end’ in En and Atsushi’s route, En tells the protagonist on the school roof that he has grown romantic feelings for someone of the same sex and asks how to deal with such situations. In which the protagonist immediately predicts the person En is suggesting is Atsushi.