Gray is sent with Natsu and Happy on a mission together, but being with Natsu, the boy he loves, and Happy makes Gray frustrated because he can't do anything about his feelings with Happy there, unless he wants to face relentless teasing, that is. When an awkward situation makes Natsu accept his feelings for Gray both of them end in a new romance.
Aka 2 doms are in a relationship and are each experienced in their own thing, Natsh being more romantic with Gray, on the other hand, being more... lustful...