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