Kimi ni Sasageru Nejirebana

In a village full of nature’s blessings, there were three childhood friends. Tiny, the hunter’s child. Thor, the village chief’s child. Sorier, the merchant’s child. They were all very close and always laughing together. ...Until they gained their gender. In this world, people gain their gender at the age of 10 and start becoming adults. Seeing Thor, who became a "boy," and Sorier, who became a "girl," Tiny begins to feel uneasy about the closeness between them. "I see, I’ve always... liked Thor." Then, on his 10th birthday, the gender the gods gave Tiny was... "boy." Realizing he is now a "boy," Tiny suppresses his feelings for Thor and distances himself from the two. At 18, after his feelings for Thor have settled, Tiny reunites with him. The feelings of "love" he had long suppressed, the responsibility of living as a "man"... The inner conflict born from gaining a gender later in life, and the future of their feelings. (Source: Pulpride, translated) Note: Includes one extra chapter.