Anri is a descendant of someone (unspecified) with Wingfield blood. From time to time those with ancestors from Wingfield will manifest properties of their heritage.

In Anri's case this is small wings that can appear on his back, and the ability to cast magic by playing the flute.

Anri's couplings all have him as the uke, and his personality is the rather girly, hesitant uke. (The creator even says it's hard for her to see him as anything but a girl.)