"Hai," he says again, looking relieved. He really, really didn't want to leave Cesare, Miquel, and especially Iago more vulnerable than necessary. Or Joker, for that matter, although he's a completely different kettle of acid-spiked candy-floss sprinkled with nutmeg and chili peppers.
Dimpling at Gaav, he pushes the fringe of his forehead to show the gold starburst of a magical brand* there. "I've always been grateful to be touched." Sobering to grimness again, although this time the vestiges of the smile stay, he says, again in a reporting tone, "It's not just my mind, though. I'd only been enough recovered even to work from serving Shard-sama** for a few years when Dynast-dono stabbed me. I think something broke off."
* This derives from those two black dots Lina hides under her headband (Xel has thicker bangs), and shows he's a Nightmare Mage.
** And this is my explanation for why he didn't show up in the first season. ;)