Definitely Enigma then. Same screenwriter/director as The Gifted, O Patha Thongpan. Compact and very well-crafted, tighter than The Gifted, like they took everything they learned there and honed it.
If you don't know the story, Baz Nattawat's film Bad Genius manages to make a real life academic cheating scandal into something of a how is this going to turn out thriller. Different feel from series of course, but worth seeking out.
Also maybe The Comments (Fon Kanittha, director for Home School). It's so well done, both in terms of messaging and for the way it reveals the many layers of its mystery. Not a thriller though.
2nd on Home School. The best made of the oppressive WTF is going on Thai high school ensemble series. The kids do pair up but there isn't much romance to it.
IMO the mystery aspect of The Eclipse isn't great and it was such a distraction from what the story is really about - very vulnerable high school boys coping (or not) with things in their lives as well as being 18 and gay. It's more relationship than romance though, if that helps, as they help each other work through things.
