I had been messing with H-KohaMech trying to figure out 214A combos.
In general, the basic form for them is
5C 5A 6AA 2[C] 214A 5C j.BC dj.BC airthrow
A harder variation is (and this is a bit character specific)
5C 5A 6AA 2[C] 214A BE5B delay 5A (that is hard) 5C 2A (whiff) 214A j.BC dj.BC
A really fucking cool variation is
5C 5A 6AA 2[C] 214A 236B(delay)A 5AC 236B(delay)A 5AC 214A j.BC dj.BC airthrow.
The first one is a lot of damage as it is and isn't too hard to confirm into, unfortunately, very often Mech-Hisui won't be in the right place and the entire combo just doesn't work. It's a shame. If you CAN confirm into it at any point though, at least doing a single 236B(delay)A loop isn't hard and you could definitely use the double loop as a bnb.
I did run her some in casuals though and I wouldn't say she's... bad, but I also don't feel she's good. Was just trying to see if I could land those combos.
I did some testing on my own time and it looks like all of H-Kohaku's battou loops work identically as H-KohaMech(she still has all of her battous including the feint). Something that I found kind of interesting is that EX battou appears to be inferior in just about every way to EX lightning grab. Both cannot be comboed off of, but it looks like every situation in which you can EX battou you can Ex 623C and get more damage and keep the same oki opportunities that Battou would give you.
Her command throw unfortunately is pretty notably inferior to H-Kohaku's, it can be comboed off of but they are allowed to tech at about halfway down the screen, making using ground moves part of the followup impossible, you're limited to a standard air combo->airthrow.
214A, 214C and 22A/B all look to be capable of leading to at minimum 4k damage combos, although 214A requires you be close enough to the wall to catch them on their way down. 22C can be used for oki and depending on spacing and timing used either to cover high/low mixups or throw attempts, however because Mech is occupied during it you CANNOT command throw during 22C, it will knock them up into the air and let them tech for free, you have to use standard throw. Much like Nero Crows->throw setups though the flamethrower still damages them during your throw, making the damage still solid even with just a normal throw.
Edit:Also her 623C has enough active frames it can be used as an air tech punish as well as jump deterrent.