Yes, this is just a woulda-shoulda-coulda thing but I think it's kind of fun to think about.
I think he should have gained new SwordTechs at certain levels as usual, but that when he could use them during battle depended on what % of life he was missing (and therefore what % he had left). This would have made him and his ability substantially more dynamic as opposed to being the antithesis of dynamic like it is now, forcing the player to basically do nothing while it charges... granted you can do some tricks just beforehand to buy a little time for a higher charge, but still.
So, example: His 1st one would be usable at 80% life left, and each successive one would require that he have 10% less life. Conveniently this puts the 8th one (same number of Techs that he has now) at 10% life left. Having such a requirement would justify making it quite powerful. Also, all previous ones would stay available, as opposed to how it is now where you can only select the one that the gauge is at.
IMO this would also add a lot of drama to pulling off the ones with steeper requirements, which I think would be another benefit. It would make Cyan a more desirable character to use, as opposed to a character that is so safe and "guaranteed" that he / she becomes kind of boring.
Lastly I think it fits the general flavor of the character... he lost his family and he's kind of like the tortured soul type in this game... so I think tying his ability into "pain" and making it so he can lash back out with it makes sense.