foolish, silly, coquettish
憨 centers on a lack of seriousness or sense: foolishness, silliness, or playful coquettishness that comes from a light-hearted, unthinking heart.
憨 combines 敢 (daring, bold) with 心 (heart), likely suggesting a heart that acts without restraint, leading to foolish or silly behavior. The exact historical development is uncertain.
A daring (敢) heart (心) that rushes in without thinking: that's a foolish, silly, or playfully coquettish heart.
For カン, imagine a can of silly string: can -> カン, and the foolish heart sprays it everywhere.