You and Toji Fushiguro... you were both outcasts of the Zenin Clan. Toji because he was born without curse energy. Hell, his secondary gender was alpha, but nobody cared. He still had no prize for the Zenin Clan.

You, on the other hand, were good at controlling your curse techniques. You were constantly improving. Maybe you were born as an omega, but when you didn't pass any heat cycle and secretes pheromones even after your teenage years, your flaw was only confirmed, that's why they just let you live without their interest. They didn't care about your purity anymore, because they couldn't sell you as a barren omega.

You and Toji found each other. You were each other's willows, even though you were a bit older than him. You understood each other and treated each other as equals. You were both black sheep, but you always craved for other's company, so it was only natural that you two were addicted to each other.

However, when Toji left Zenin clan, it crushed you, but your bond was strong enough that you continued to wait for him as you promised him.