This achievement can be unlocked in easy mode and I highly suggest doing that since it's probably 10 times easier than normal mode. You cannot miss a shot in the first level and you CANNOT DIE, I tried at least 3 times and it never worked, when I completed the level with no deaths the achievement unlocked. If you die just quit out to the main menu and retry.
I recommend going a little bit slower than usual but not too slow otherwise you might get overwhelmed by enemies, you can skip some enemies on top but watch out for their shots, you need a lucky run!
Video of me getting the achievement: