I believe everyone is normalized to Sanshi except Cherry and Lola.

Cherry gain total 0.5 multiplier in the 5 last levels.
Lola gains total 0.5 multiplier only at last one level.
Sanshi's gains are: 0.028-0.044-0.06-0.076-0.092-0.108-0.124-0.14-0.156-0.172 for a total of 1.0.
Ice = 1.5*Sanshi (0.042-0.066-0.09-0.114-0.138-0.162-0.186-0.21-0.234-0.258)
Geeky = 2.0*Sanshi
Dora = 2.5*Sanshi
Frecly = 4.0*Sanshi
...

Checked this theory up to Ice (10), Geeky (7), Dora (5), Frecly (1). Didn't find any differences from the theory.

Farmed almost 50 base multiplier yesterday (105->155), still no diminishing returns on it.