User blog comment:Maki Kuronami/Lesson 26: UNDERGROUND CRIMES IN UNDERGROUND CITY/@comment-25110963-20141010020232/@comment-10380701-20141010021738

It has a club-like design, so I assume it's blunt, or the thermos can heat itself up, turning it into a flaming club of fiery dooms.

Likely the heater is a Fire Dust. That makes it a veeery clever usage of Dust.