Being trans here exists in the context of an omegaverse and a sub/dom universe. Acc the manga it’s usually dom/sub mental genders that have developed alongside the physical a/b/o genders, with alphas usually being doms and omegas being subs. However the lead couple here are a sub alpha and a dom omega, so in the context of the manga they’re both transgender (and the same is stated in the text of the manga in chapter 2).

Transman realness <3 <3 <3