Vol. 4 Stream sketches so many stream sketches, why stream sketches?

Vol. 1: pixiv #97394342 »
Vol. 2: pixiv #99469153 »
Vol. 3: pixiv #101652846 »

Rapidin 2021:
pixiv #88966925 »
pixiv #90950194 »
pixiv #93153633 »
pixiv #95257445 »