Shinai Shinai mo Ai no Uchi

Hayato, an Alpha, had been troubled by the same concern for years. Despite being fated mates (ban) with his older childhood friend, the Omega Riiichi, their relationship had never progressed beyond a kiss. Nine years ago, when Hayato was still a child, he accidentally bit Riiichi's nape while playing around, unintentionally forming a lifelong bond. Because of this, Riiichi made Hayato promise not to cross any lines until he became an adult. With only one year left until he turns 20, Hayato is determined to win Riiichi's heart before then! He starts taking action, but every attempt seems to end in failure... or so he thought!? Riiichi had always seen him as a child, but when Hayato’s now-mature hands touch him gently, his self-control begins to crumble…?

(Source: KiR comics, translated)