Chord sequence
B♭m7 Gm7♭5 Cm7♭5 B7♯11
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in Bb minor
Over Bbm7 · i7
Mode 2 of Major
Over Gm7b5 · viø7
Mode 7 of Major
Over Cm7b5 · iiø7
Over B7#11 · subV7♯11
Mode 4 of Melodic Minor