Av1an's vapoursynth script generation mechanism couldn't handle special punctuation (e.g. ： , fullwidth colon) in file path,
using raw path (i.e. core.ffms2.Source(r"<PATH HERE>", cachefile=r"<PATH HERE>"))
seems to solve the problem
more work should be done though, as those punctuation seemed to be automatically replaced to "\u{xxx}" form
e.g. "コスプレ" (cosplay) would become "コスフ\u{309a}レ"