Deneb

Deneb, "The Swan", is a Silver Key Celestial Spirit that is under a contract with Yukino Aguria.

He is summoned by Yukino while facing Eclipse Mother Pisces, who is traveling through a water tunnel she created. Deneb says he doesn't need their sympathy as to why his wings aren't white but Levy responds she wasn't thinking that. Yukino tells Deneb to find Mother Pisces and fight her but he says that telling him to do his best has the opposite effect. Eclipse Mother Pisces appears behind the two girls and Yukino tells Deneb he doesn't have to do his best, causing him to do the opposite and try his best by using Summer Triangle, sending Mother Pisces flying. Levy praises him and Deneb leaves thinking it is annoying

(Source: Fairy Tail Wiki)