Ruiner

I would recommend doing this with the Energy Shield ability (you unlock this earlier), but you can also do this achievement with the Kinetic Barrier. You can find both of these in the first row of the abilities section BUT you must upgrade either to it's second stage (under Energy shield it's called "Deflective Shield", under Kinetic Barrier it's called "Reactive Barrier".

After upgrading, simply deflect 100 bullets with either and the achievement will be yours. This is cumulative, so no worries about dying (this game is tough as nails at times).

If you have any concerns or suggestions, lemme know!