I haven't watched Happiness. But I think:
King2Hearts Ennemies to allies to lovers, they are both in the military and there's quite a few action scenes and a lot of romance.
Kill It The romance is barely there (almost not, aka no kiss) but there's quite a lot of chemistry.
Keun Ruk Salub Chata The leads are put in dangerous situations and often need to defend each other. There's also a mystery and some family elements.
Bromance the ML is the leader of a mafia family and the FL becomes his right hand man. That being said, the mafia aspect isn't realistically protrayed at all (they're nice and cute).
Cruel Romance mafia family too, but more realistic.
Kor Kerd Mai Klai Klai Ter somebody's trying to kill them and they have to fight back. Especially the FL who's a badass pilot.