Yeah, that is what I thought after hearing more about him. I will approve as long as you make the heat energy absorption more of a clear thing and you will also have to get @Kronshi approval of course.
The reason I asked is because if he joined Bloodstone's side than Ambers power is null which isn't a bad thing since we have a lot of gems on the Crystal side however, if he was on the Crystal side...it would be like a major cheat cause Amber controls fire and Mars would run on heat but now that you describe him a bit, he would never let Amber do that because of the whole pride thing.
If he can only absorb heat based attacks not all energy that is a bit better. I think you need to state that more clearly though because it does no come across that way and energy manipulation is a big power most of the time. The limitation of certain powers does help with some of my worries on the matter since you already did well in stating how the power is released and that releasing all of it is bad and doesn't last long.
The big worry now has to do with this question, what side will he be on? It is retaliative and important, I will explain why in a moment.
Energy is energy. Being able to absorb means all forms and the more energy you have the more damage you can do. This is where the realm of over power begins. Yes he has to stay still and focus but if he is always storing and releasing then he has a lot of room to absorb any big attack. He could lose focus for a split second but then he has weapons to fall back on quickly or taking that absorbed energy and just using it in whatever way he wants.
See what I am saying? There isn't much of a down fall. The only down fall is always having to release energy which isn't much of a down fall.
Energy manipulation is always kind of a sticky area because it is incredibly hard to hurt that kind of being because they adsorb the damage if they are about to get hurt and if they get close to their limit then they just get rid of the energy or start using it in a different way so they can absorb while they are doing that. It just seems like it will get to either an over powering point or you will have to hold back all the time which is no fun for you.