Project Sekai: Colorful Stage - Airi x Ena

A classic "childhood friends" trope. Admittedly, this one does feel a lot more platonic than romantic to me. With that said, they both have vaguely similar temperaments and are touched by at least a bit of the "tsun" (Ena more so than Airi). It's a very genuine relationship between two people who can probably say anything to each other and still remain friends.