This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
虝 combines 虎 (tiger) with 勿, but the exact historical development and original meaning are uncertain.
The tiger enclosure 虎 wraps around 勿, but the meaning is unclear. Think of a tiger that should not be approached.
For コ, imagine a tiger cub (こ) hiding inside the enclosure: こ -> コ, and the cub is the small thing inside the tiger shape.