For starters, I’d recommend starting almost all combos with this instead: cr.MK->mp rekka->rekka hits of choice->QCB+P linker. Hisako’s heavies are good buttons, but are pretty slow in general. Crouch MK is a much faster button with slightly less range, but is also a low, which lets you catch people who aren’t watching their toes. Going immediately from the rekka opener into influence linker will also help generate timing lockouts, particularly on any opponent who is mashing breaker.
Welcome to KI and Hisako. Hope you have fun! 