6-gatsu no Nanahoshi

Up-and-coming pitcher Kanata Saiga is a battery together with his childhood friend Haruse Shinonome, who is also the baseball team captain and catcher. When they were kids, Haruse, who just moved into the neighborhood, started talking to the introverted Kanata. Ever since then, they grew up together like brothers: Haruse as the "older brother", and Kanata as the "younger brother". However, Kanata pines and lusts for his "older brother". Kanata broods, wondering how long their pretend-play at brothers will continue...

(Source: Gentosha Comics, translated)