It's probably from the cold. He took him out of the water too fast. Midnighter tries to cover it with his own bulk, with the body that always runs hot, that saved him from the freeze just hours ago. He pets Nyx's hair and kisses his face, wrapping himself up in his arms. "Slow or fast? However you want it. Gonna give you everything good, baby. Mean it. Everything I got, s'yours."