I believe that I had previously wrote about the possibility of energy beings, although it seems that them being made of neutrinos is right out. So I instead thought of them being made of plasma. Some sources indeed consider the possibility of plasma-based lifeforms, and that they were existent in the very early ages of the planet. Here are some details of this made by David Darling.
I need not have this setting be so hard in scientific authenticity, and I imagine that they can not only have long lives, at least in hot areas like stars (they would most likely dissipate quickly in current Earth-like conditions), but can be macroscopic in nature, ranging from the size of insects, or even human bodies.
However, one part that I still want to keep the "hard science" is how these plasma lifeforms interact with physical matter. What type of senses do they have? How do they see, hear and touch physical matter? Can they even have these senses at all?