To those who don't know, there are chemicals (Stronger Enememine=テキツヨメミン and Weaker Enememine= テキヨワメミン) you can buy from the Chimera Research lab. One makes enemies weaker and the other makes enemies stronger (obviously). These also half or double the amount of EXP enemies give out.
Going back to Sunshine Forest to use one. You should reach Level 99 if you stick to the plan.