warming one's crotch over a hibachi
Historical term for a practice of standing over a charcoal brazier (hibachi) to warm the lower body. Rare in modern usage; mainly encountered in descriptions of old Japanese daily life.
In old Japan, people sometimes warmed themselves by standing over a hibachi on cold days.
Compound of 股 (mata, 'crotch') and 火 (hi, 'fire'), referring to the practice of warming the crotch area over a fire. The exact historical origin is uncertain.