So, I’m trying to come up with a concept that resolves a special energy that gives people powers. When they die, their energy still remains. The energy can be crystallized to honor the deceased. However, the crystallized energy can still be used as a source or increase one’s own power if fallen in the wrong hands. My dilemma is this lore concept sounds so similar to the Final Fantasy games, particularly VII. I played and enjoyed the hell of it. Does this sound too similar?
As Final Fantasy Fan myself, I wouldn't say that it is bad.
As writer I would say: It depends on your story. Is the story similar to Final Fantasy VII? Do you have a similar setting? Do people use the power in similar ways?
If you take a closer look at the concept of magic, you often have a similar source (Mana or Chi) to cast spells. The difference between them is the source, the origin and the past.
The source and the origin
Where did your energy started? Created by an higher being? Was it there the whole time? How did your power started?
What happened in the past with your power? There weren't nice guys around until your conflict happened. So how was your power used in the past?
Try to differentiate your story from that of FF. You can't recreate the wheel, but you can design it in your way.