Overflow Points

Overflow Points are the reward given for completing Overflow Challenge.

You can use overflow points to buy various perks:

The cost for the next level is (base cost)*(num bought + 1)

Because of the cost increase, it's generally hard to spend all your points in one area and better to mostly spread them around. Buying more levels of BH/BHU is very helpful in 12hr+ rebirths and shorter rebirths where you can cap your GP from BHU. Going heavier on CP, CS, and CC when available is generally a good plan for long-term spending.