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