Small bottle of everlasting fire

A small bottle containing an everlasting fire that acts like a familiar. Protects its holder by damaging an attacking foe by 1d4, after a d20 against AC roll, when the holder is being attacked.

The everlasting fire is upgradable by feeding it small doses of burnable material every so often, which would make that after a while, in conjunction to the players level, can be upgraded to 1d6, 1d8 etc.