Syuu Nanao

Nanao Syuu, is one of Aiba's friends in N.I.D.F. He has the same surname as Aiba, Syuu, pronounced as Shu. This, and him being around Yuno who loves Aiba, whom she calls Shu. And his unannounced affection towards her causes his actions and behaviors after Yuno lost her memories, Yuno thought that she had killed "Shu", at the time he couldn't do anything but claim that he was Shu, to ease her suffering.

Later in the series, the tension between Aiba and Nanao is mainly due to the latter's action to ease Yuno's pain who he secretly loves, but in the end trying become Yuno's "Shu".