AruAni

AruAni is the het ship between Armin Arlert and Annie Leonhardt from the Attack on Titan fandom.

Canon
Annie spared Armin's Life twice whilst in Titan form, even though she slayed everyone else. Annie was probably aware that he would be able to identify her since he's very smart.

Armin emotionally blackmailed Annie into working with them even though she knew it was a trap, thus implying they got close enough for him to know how to get under her skin. More than Eren, who is noted to have been getting combat lessons from Annie.

Armin waited two months before saying anything about the female titan's identity because he wanted to be wrong for once.

Once again, during the rematch of Eren vs Annie, Annie spares Armin's life. He tells her that if she can't kill him here and now that she "can't keep using the same bullshit lie that your bet is just beginning," yet she turns away and ignores him.