I found a cover of Donut Hole by Kettaro on youtube and took a look to see if it was him. Turns out it was, and he collaborated with someone I don't remember who. I remember distinctly that the PV (?) was re-done to make it unique to him and the person he collaborated with. I tried to find the video again but I'm not sure if it was deleted orz
Maybe I missed it out but I checked a couple of times on the list of songs he covered and didn't find it on the list. Did he delete the cover, or is it buried underneath all the new covers and songs?