1) Hyuk/Ken 
Jaehwan accidentally drops his family ring into a lake and the pesky mermaid who lives in it won't give it back. (Mermaid Au)

2) Ravi/Ken
 In which Ravi is sent to the moon to kill a princess, but ends up rescuing a prince. (On and On space au)

3) Hongbin/Ken
Prom night in a normal school can end as disasters, prom night in a school of supernaturals can end with half the building levelled, Hongbin in a dress and Jaehwan nearly burnt at stake. (Moorim Inspired, though I have never watched Moorim)

4) Leo/Ken
When his grandfather's will said he would be inheriting a special heirloom along with the house, Jaehwan envisioned gold or priceless antiquities, not the ghost of one Jung Taekwoon. (Ghost Au)

5) N/Ken
Hakyeon neglected to mention that he was a wizard, and that Jaehwan shouldn't be drinking his wolfsbane potions. (Werewolf AU)