Samurai's Kenki Gauge requires very little thought, some suggestions to improve it:

Because all of your main Kenki spenders cost only 25 Kenki, it feels almost impossible to not have enough Kenki for skills like Hissatsu: Senei or your gap closer when you need them. This means that essentially the only management of Samurai's Kenki gauge you really have to pay attention to is making sure you don't cap on Kenki, which is the bare minimum that ANY gauge requires.

Zanshin theoretically might make this more interesting, except it is exclusively tied to a skill which gives you the 50 Kenki needed to use it. If we could use Zanshin more frequently, it might make the Kenki gauge a bit more interesting. Perhaps we could be given the "Zanshin Ready" status after every Iajutsu? Or a different skill? Or it could always be separated and given its own cooldown.

It goes without saying, but Kaiten also fulfilled this role.

I think even something like increasing the damage and Kenki cost of your gap closer Hissatsu: Gyoten would be FANTASTIC. If it cost 20 Kenki then you might have to plan around it a bit. Currently, at only 10 Kenki, it feels borderline impossible to not have enough Kenki needed to use it.

Anyways, I hope feedback on Samurai's Kenki gauge is taken into consideration in the future.