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