Secret Debut Duo

Summary: After it was resolved Oneus have been thinking about their next album plans and songs. Xion, meanwhile, wanted to do a solo and a duet. He was unsure about his solo song until he listened to one of their songs and decided to sing it, except tweaking it. Which song will Xion be singing? How will it be tweaked? Who will Xion do a duet with? And more importantly, where and when will Xion be singing it?