I have already mentioned this song in the Touhou cross-overs section, but I think this thread might be even better
Scarlet Sky - Original Touhou Fan Song feat. TALI, Kylee Brielle
This song has been quite a surprise for me. Stringstorm, the creator of this thing, is already known in for his original songs themed around the universe of Warhammer 40.000. However, since last summer, due to a series of screw-up on the side of the IP owners of Warhammer in terms of fan-made content he has started exploring other series including BattleTech or making cheeky 40K parodies. However, he has also made a Touhou song. Most (myself included) would think this is the first time he delved into the wonderful universe of Gensokyo, but this is actually the second time. On 9/9/2019, Stringstorm made a metal cover for GO CIRCLE NINE. This song might seem weird for some, but I think the explanation is that this is an original song, not base on anything already existent. However, as he declared he likes this series, and the fact he basically stumbled upon a gold mine, we can expect more Touhou original songs in the future.
All I want to say about Scarlet Sky is that, as the name suggests, is a retelling of the story from Touhou 6, from the perspective of Reimu.