All my confusion began while thinking of can charge be related to energy. Now Coulomb's law state that two body having some charges apply forces on each other which is true. And according to Newton $F=ma$ means force can be exerted on a body having some mass. Since charges apply forces so it should not possible that they exist without mass! Either it is negligible, but there should some mass if charge exists but that shouldn't be zero.
Now $F=k\frac{q_1q_2}{r^2}=ma$ where $F$ is force on $q_2$ of mass $m$ due to $q_1$. Now if we start converting mass $m$ into energy keeping $q_1$ fixed at it's position and $q_1$ constant, the acceleration of the mass will increases and charge $q_2$ will be there on the mass till traces of $m$ exists and making force due to charges constant, by this concept I concluded that any amount of charge can exist on any amount of mass means $1\,\text{C}$ of charge can exist on a body of mass of order $10\,\text{kg}$ or $10\,\text{mg}$ or $10\,\text{ng}$.
Now coming to point that if I take a mass and given it some net charge $q$ and started converting that mass into energy (somehow) till that mass completely gets converted into energy so that no mass exist for the charge to gather on, then where should that charge $q$ will go, will it get destroyed or it also gets converted into energy? If it gets converted into energy then there shouldn't some more energy released rather than $mc^2$
This is my approach to prove $E=mc^2$ hope someone will tell me what I am missing or may be I am right!