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