Here is the full list of all 20 Kaiju Princess achievements.
Reach Mouth Accomplishment Lv.3
Obtain the Bikini
Kisses x1000
Reach Vagina Accomplishment Lv.3
Reach Breast Accomplishment Lv.3
Reach Clit Accomplishment Lv.3
Reach Orgasm x8
Obtain the Magical Teen Outfit
Reach Orgasm x4
Obtain the Maid Outfit
Obtain Black Cat Cape Doll
Reach Orgasm x2
Obtain Tilapia Doll
Obtain the Competition Swimsuit
Obtain Festival Fan Doll
Obtain Popsicle Kaiju Doll
First Quota Reached
Cum with Me
Obtain the Witch Outfit
First Time