That's his fiesty, beautiful lover, the one only Gladio knows avout, and he likes it that way. They two of them meet each other's needs so well, and Gladio shows his appreciation by leaning in for a brief, warm kiss first.

Then, with a promise to give to the other, he drops to his knees. Rucking up Ignis' shirt wirh his hands as he presses kisses to skin being revealed, fingers wandering toward his belt to undo. The upcoming full moon might have a bit of a hand in them choosing to do this in the kirchen, but it is Gladio's adoration and love for the other that make him want to please him, rather than selfishly breed him.