Rally

Rally is a mechanic that is engaged whenever Kit takes damage. 40% of any damage(80% if using the Griseus Special MK.II) is also put into Rally which can be used to recover HP by using any Rally-Enabled weapon and damaging enemies while those weapons are held. You can even shoot with a Non-Rally weapon and switch to a Rally weapon to get health back.

Rally-Enabled Weapons
A.R.C Blade Raikiri Griseus Special MK.II