Overview
Carcano M91/38 is a non-elite obliteration specialist.
Carcano M91/38 deals immense damage to beefy high priority non-elite targets. This skillshot targets the highest HP enemy, so some care needs to be taken when bringing her against newer enemy teams as she could get stuck shooting elite enemies. Even if there are no big non-elite targets and she massively overkills smaller ones, her general performance is in line with most other 5☆ RFs. As a result, raising her early is not a problem, though a generalist RF would still be preferred for mobbing. It should be noted that the majority of bigger (non-boss) enemies are not elite, and a full list of enemies and their tags
can be found here.
With this in mind, Carcano M91/38 is very highly recommended to raise.
Carcano M91/38’s Event SPEQ gives her +4 Rate of Fire, and grants her small Damage buffs when receiving RoF buffs. Overall, this doesn’t change how she is used at all, but it is certainly not bad either.
Her sister’s Ranking SPEQ allows Carcano M91/38 to deal full damage to all enemies, and can be considered if very specific Elite enemies are causing problems with Teambuilding, but should not be an immediate inclusion if you intend to use Carcano M91/38.
The damage buffs from Carcano M91/38’s Event SPEQ should generally just be considered a nice bonus when you need to use her sister for Elite tag removal, and not a reason to always pair them together.