Wise Turtle Publishing

I'm considering using OVA as a replacement rule system for a game featuring Teenage psychics. One of the things I need to consider is how to make psionic abilities a finite resource (the original game used Psi Points) and it seems like making psychic abilities use a minimum of 1 endurance per use.

That's not the real issue though. One of the big things from the original game is that each use of a power uses up part of an "Overflow Gauge" when its all used up the esper undergoes Overload. Basically, the go full-blown Tetsuo loosing all control of their abilities and lashing out at everyone and everything around them in the messiest, most violent way possible. Telekinetics rend, smash, crush and implode their surroundings. Thermokinetics incinerate everything around them in a pyrokinetic firestorm. Psychokinetics emite psychic vibrations the melt peoples brains and cause their heads to explode. Overloading is also usually fatal to the psychic as well.

How is the best way to represent the above?

A quick glance-through of the book's Weaknesses and Flaws list don't really have anything handy by RAW. You'll have to design a Unique Weakness or a Unique Flaw to get the effect that you like.

You could use Miho's Self Preservation Mode as guide. (Basically a Transformation with a Trigger and a Unique Weakness for loss of control.)