Wise Turtle Publishing

It looks like health and endurance are almost the same things. If one is 0 you get a -1 penalty to all actions. Both need to be 0 to go unconcious.
But endurance is used to cast/do all kinds of power moves and spells etc.

So why not always take some levels of Frail and use those points to buy levels of Vitality? This way, you may get a health of 0 quickly and get the -1 penalty. But you can keep doing those power moves and spells.

(This is mainly looking from a combat point of view. Maybe in normal situations other than combat you're character would look really frail and weak wich would give other complications?)

The main reason is if your Health is really low, you can take one major hit and instantly be down to a -1 Penalty. Unlike Endurance draining abilities, taking damage is something you have no control over. You can stop casting spells before you hit a -1 Penalty, and even if you spent the whole shebang, you can always rest a round and gain at least 5 back. Once you lose your Health, that -1 Penalty is there to stay.

In the end, one is probably not better than the other. It's all a matter of give and take. Do you want to have a vast store of energy for attacks, or be able to fight at full capacity for as long as possible? So to answer your question, there IS no reason why you can't do that. In fact, I expect many elderly mage characters follow a similar MO. (Unless they're also drunken karate masters...)

And as you mentioned, these attributes have very different non-combat applications as well.

Personally I am not too keen of the rules that allow you to swap Health/Encurance when you reach zero on one of them. If weakens the distinction between the two. I would prefer a rule more along the lines of Zero Health=Unconsciousness, Zero Endurance=No more End spending.

The idea was, as with many other rules in OVA, to maintain the spirit of anime. Characters completely drained of spiritual power can continue casting spells, raising barriers, etc. at the expense of their own health (even to the point of dying.) Likewise characters can continuously take a beating long after their physical fortitude should have worn out. It's a theme we see time and time again.

Obviously, if you want something more realistic, you might want to make a clean division of the two. It's a simple tailor to make and (as far as I know) won't break the game.