Best girl Airi... without saying what makes her best girl (watch this episode and you'll understand) there's an interesting theory among Boku Dake (Erased) fans, and this episode contributes to the speculation. It's that Airi is Kayo, reincarnated. Consider that Airi is 11 years younger than Satoru (she's 17, he's 28 or 29). So Airi was born right after Kayo was killed. Supporting this claim is that both girls call Satoru an idiot, and Airi does somewhat resemble Kayo. It's suggested that Satoru was drawn to Airi because she subconsciously reminded him of Kayo, who his mother had tried to make him forget. I don't think this is actually true, it's just one of those things, like Satoru's revivals, that makes the story different.