Well Shinsou Wotan might be right but who knows...he might be her other brother or something of the sort, or Yuki's husband, if they took her last name.
I doun't think he can be her father tought...he looks way too young..
Yuki would only be 19 as she was 12 or something in Liminality, not impossible, though not plausible. It also is not strange it seems in Japan to take the wife's last name, in my opinion it is the ultimate sign of respect for a wife.
well, he does look like the "playa" type... sort of... so the kanji for "love" in his name might just be some kinda screen name type of thing, like how many celebrities change their name so it'll be more catchy. But yeah, he's probably of no relation to Yuki.
But usually when they do that they make their last name be more more foreign, like with Tomiko Van and Yusuke Santa Maria... I think with being from Brazil he already has his bases covered...