So, ever since Povynn and Emronia have been around, people have been asking themselves "Well, who's the third member of your trio?", assuming that we're supposed to make out a trio just like the original Lake Trio.
Well, I got some good news for you, we are a trio!
This is the third member of the trio, his name is Quentin, he's around the same age as Emronia, which means he's on his early/mid 20s by the time PMD: Starscape Weaver and Skygardening happen. He comes from the same town that Emronia used to live before she was sent to the PMD world, and, because of that, he's been a longtime friend of hers.

As for what kind of lakesprit he is, it's sort of ambiguous, just like Povynn.

This pic was also posted today in celebration of Lakesprit day (March 21), which hasn't started where I live, but, it did start in Japan, which is where this holiday (it's a holiday according to me!) was coined.

Art and Quentin by me.