(there's too many gems in the hyunchan tag this answer is long sorry anon i can't contain myself)
FIRST OF ALL these two, they're the OG hyunchan bibles must read, theyre long tho. kingdoms apart is finished, hold you is unfortunately not but these were formative to the early hyunchan fandom and i think every hyunchanner must read these:

https://archiveofourown.org/works/28665117

https://archiveofourown.org/series/2252255

this is the canon compliant red lights fic, rite of passage for every hyunchanner as well: https://archiveofourown.org/works/33876919

apart from that, my favourites in no particular order:
https://archiveofourown.org/works/41022525
https://archiveofourown.org/works/58704883
https://archiveofourown.org/works/36909157
https://archiveofourown.org/works/48483205
https://archiveofourown.org/works/42170148
https://archiveofourown.org/works/43551117
https://archiveofourown.org/works/43497705
https://archiveofourown.org/works/40485906
https://archiveofourown.org/works/60105925
https://archiveofourown.org/works/49282720
https://archiveofourown.org/works/51282058
https://archiveofourown.org/works/33876919
https://archiveofourown.org/works/48916783
https://archiveofourown.org/works/59460307

there's def a LOT more im missing,, and sorry i didnt provide any descriptions cuz im at work skdhkdd but also,,, you could also read my fics hehe i would def throw 'chained hearts' your way <3 (https://archiveofourown.org/works/69434371)

hope you enjoy reading them!!