Tomodachi no Neechan ni Koishita Hanashi  

Tomodachi no Nee-chan ni Koishita

Rio is everything that Haruto wants in a girl: gentle, nurturing, and ladylike. The only problem is that shes the older sister of his best buddy Nao, and he fears that the difference in age means hes barely on her radar. If Haruto wants Rio to see him as more than her little brothers playmate, then he has to prove himself as a man in her eyes, no matter what it takes.(Source: Irodori Comics)