He's EMIYA (Assassin). He's a demi-Servant fusion of Kiritsugu and EMIYA, which is why he's got the dark skin and white hair.
That was bullcrap people made up when we didn't know anything about him but the appearance. He's just the alternate Kerry from the Fate/Accel Zero Order abnormal singularity, that got hired as counter guardian instead of getting into the Zero plot.
He tried calling tech support about his SWAG being stuck at ''on'' but it seems he is going to be on hold for while.
You know, if I was surrounded by four affectionate and beautiful women who all have the sweet voice of Sayaka Ohara, I think I could delay my call to tech support and just enjoy the situation for a while longer.
This is made even more awkward when you realize that he is a completely different Kiritsugu
And thus has completely no idea as to why Irisviel is acting the way she is
He has some inkling, even if he wasn't a counter guardian being forced by Ayala to hunt Iri down, their destinies are intricately linked regardless of timelines. They would have met in one way or another.