Go fusion
With a compact fusion device, you could make the VTOL aircraft as big as you wanted since power output is no longer a limitation. The heavy penalties associated with shielding fission reactions don't appear in fusion reactions. Two benefits of fusion is that first, the result are beoutput is a stream of alpha particles and second, fusion reactions yield more energy than fission reactions. These are easily turned into electric current and can be shielded with a few inches of air or human skin. Paper is also cited as an effective shield for alpha particles.
Fusion is hard
We don't have a way to make fusion power plants yet, compact or otherwise, because it's really difficult. Humanity has been working on the problem for 60 years and still haven't cracked it. I have a question over on Physics SE to see if someone can point me towards an interesting approach that I haven't heard about in long time that was supposed to be clean, powerful and light on radiation.
The VTOL would have to be built around the fusion plant but on a larger craft more options are available in where to place the power plant. Perhaps a craft reminiscent of the V-22 OspreyV-22 Osprey with tilt rotors for VTOL operations, might do the trick. Just trade out the turboprops for electric motors feed by the fusion power plant.