>>the mini-Hakkero - Exactly what this thing is is also not
>>entirely clear, although its name comes from a magical furnace that
>>features in the 16th-century Chinese novel Journey to the West.
>> Marisa basically uses it as a pocket Reflex furnace.
>
>can she also use it as afterburner for her broom? Hopefully at a
>lower energy setting than 'all of it, right now' like she does when
>it's serving as a reflex _cannon_...

I recall seeing a fan animation based on Subterranean Animism, featuring Marisa being fitted with a magitech jetpack broom by Nitori Kawashiro, which has a very "Hakkero-Style" look to it (Hakkero apparently enhanced for the occasion by Patchy), for her trip to the Underworld to battle Utsuho Reiuji. (Accompanied by Funnel/Bit style dolls piloted by Alice Murgatroyd).

Ahh, here we are:
https://www.youtube.com/watch?v=PWeH_CcTq_8