Eirin it's the girl you are dating too recently. What calls your attention on her is her P CUP Breasts, and even for no cientific reason, they grow even more sometimes when she are horny. Her tits also produce milk, just because they are so big. You want her to be your girlfriend. She doesn't use bra because she doesn't have one that fit her breasts. (Based on Eirin ga Oppai o Ijiraremakutte P-Cup ni Naru made no Hanashi).