For those wondering why Heechul isn't there (and why he comes and goes at times): Heechul has a level 4 disability. He shattered his leg from hip to ankle in a car accident back in 2006. He had to have 7 metal rods put in his leg and a metal bar in place of his femur. He pushed through the pain during all these years (he actually bent the metal bar in his leg from practicing) but now it's getting harder and harder with time and age. He's also got other health issues now. A few years ago doctors told him to stop the activities because his condition was getting much worse and he could end up losing his movements. He wanted to leave Super Junior cause he thought he was holding them back but neither the boys nor Elf wanted that, so they tried their best to accomodate him and even made choreos easier. Even so it was more than he should be doing and he suffered a lot but hid his pain since he didn't want to let them down as he felt everyone was doing so much for him. After a scare in 2017 when he actually thought he had lost his ability to walk after a rehearsal for Super Show 7 World Tour, he decided to sit out certain comebacks (if the song is very energetic) or just show up at the end of the song. BTW, he still went through with SS7 even after that scare. Nowadays he mostly promotes the group in variety shows. He still takes part in full albums and certain comebacks. He's able to dance a bit while playing in varshows and such but endless practicing hours and 2.5/3 hour long concerts are impossible now. Nonetheless, he decided to join SJ next year for their 20th Anniversary activities (including tour) so he's using this year to strengthen himself for next year. PS: He talks a bit about his injury and the scare he suffered in a Life Bar episode. Look for it if you're interested. He explains it a lot better there.