Well, I am thinking a Hikki song that sounded like another song to be mixed, and I come up with the following songs:

-Addicted To You (Underwater Mix) and Janet Jackson's "That's The Way Love Goes" (It sounds very similar, especially the guitar part and some chorus as well)

-Kairo and Super Junior's "Sorry, Sorry - Answer" (the string sections in the chorus of Kairo as well as the chorus itself)

-Come Back To Me and Mariah Carey's "We Belong Together"

-This Is Love and Kangta's "Breaka Shaka"

Can you think of other Hikki songs that can be mixed or fit in to another song?