If you had to put Da On in a seme or uke box, outside of his relationship with Tae Kyung, which would you and why?
Not that I'm entirely convinced either would apply to him; I simply find his character interesting and want to explore it. If you don't think he belongs in either box feel free to expand upon that as well.
I don't think he belongs in either. He just needs a mutual care relationship. He also reads as a little bi and a little demi or something? I think he just needs more time spent finding himself before he (or we) know what he is or wants in another person.
However, if he were to be in a BL narrative he'd be fun to give a coming of age seme narrative. Like him learning how to be a seme. He could be one of those who needs to be taken care of but also needs to care, like how a pet can help save a broken person. The act of caring in and of itself can be healing. In which case he needs another capable but lost soul, like Kaitoon (in currently running Love Area). No full time fragility like, say Pharm. DaOn isn't capable of being overbearing to the extent that traditional yaoi ukes require.
That said he is a such a good boy, some seme could come along and just get off on spoiling him with focused attention and total care to the exclusion of the rest of the world and DaOn might crumble for that. I'm thinking of Nubsib's style in Lovely Writer. Like some glowering edgy bad boy type who would force him to relax and loosen up (all the puns intended).