I was most disappointed after it failed to appear in the first episode of the Persona 4 anime, but the second episode provided the goods! Sure, it doesn’t actually say “Mikan”, but given prior evidence I’m going to claim it.

(As a vaguely related side-note, it’s kind of disappointing that, for a film set in a region where Mandarins are farmed, and featuring an number of Mandarin farmers, A Letter For Momo doesn’t have a single obvious Mikan Box in it. I think I might have spotted one at one point, but it’s going to be a loooooooong wait to check).