Board Thread:Questions and Answers/@comment-28196331-20161011050100/@comment-28572671-20161111172727

I'd say "ambiguously gay " would fit more.

While the producers of the anime confirmed they see Mika's feelings for Yuu as romantic, Kagami has yet to talk about their sexualities or give valid hints (aside from a llittle teasing here and there ).

I do believe Mika is constantly implied to have feelings for him, and while Yuu is quite more affectionate with him (he even said he was glad he kept living because he got to see him again??) than with other people, this could still be pure baiting. Kagami Takaya has used homoerotic undertones in his past works, but if I remember correctly, it was all meant to attract more audience and nothing more.

Yuu is not confirmed to be homosexual, but he's not confirmed to be heterosexual either, if you want to see it that way.

As Kagami said when he was questioned whether or not they'll be a couple at Germany's Q&A:

It's up to your interpretation.