Finding it kind of interesting to look into Touhou songs that directly parody/take inspiration from non-Touhou tracks. For example here, Gate of Forbidden, obviously a take on Hacking to the Gate.
https://inv.nadeko.net/watch?v=IpFTtqWM-JQ
The Touhou wiki has something of a list of these, but it's damn hard to find as it's not directly linked anywhere and hardly maintained. Still, there's quite a few interesting and high quality ones on the list as it is. SOUND HOLIC's chireiden focused Kemono Friends parody is always real fun, as is Pan Pan Panty.
https://en.touhouwiki.net/wiki/Touhou_Arrangement_Parodies