If the work is a lyricized version of a Touhou song, then “based on” should probably be the relationship to use. If it is just a direct arrangement, then just use the original work with a cover relationship instead.
A cover relationship is definitely appropriate for recordings that essentially use the original composition (e.g., Akyu’s Untouched Score, Romantique Tp’s MIDI recordings), but most Touhou music reworks the source material quite significantly – even the tracks without vocals. e.g. izna’s “Super Fine Red” is no more a cover of “上海紅茶館 ～ Chinese Tea” than EastNewSound’s “STAY HERE, NOT ALONE”.
All three are distinct works, and the two derivative works both significantly alter the original composition. But are they enough of a departure from the original that they’re no longer even “arrangements” of it?
One idea I had, at least as a rule of thumb, is to let the artist decide: if the liner notes credit ZUN (or another soundtrack composer) for the composition, then the metadata should mark it as an arrangement of his composition. Otherwise, it’s based on it.
How does that sound?
It’s standard practise on Touhou works to credit ZUN (or U2/あきやまうに) for composition even if very little of the original survives in the arrangement, so that’s not really a useful way to tell the difference.
There’s two cases where we need to create a new work:
- Additional composition or lyrics credits are added
- There are multiple recordings of the same arrangement, and we want to link them together
In other cases, we should link the recording back to the original work as a cover.
The guidelines for classical works helped me understand where you’re coming from here:
For an arrangement to be valid as a unique work in MusicBrainz, it must be possible for other performers to record new versions. There must be at least two different recordings available. The recordings must be of different performances by two different (groups of) performers. You must be able to source that the both performances use the exact same arrangement. If in doubt, do not create a new work.
So I’ll reserve new works for the conditions you suggest, and use “based on” rather than “arrangement of” as CyberSkull suggests. Thanks!