Here is the full list of all 20 Kaiju Princess achievements.
Reach Mouth Accomplishment Lv.3
Obtain the Magical Teen Outfit
Obtain the Bikini
Obtain the Maid Outfit
Reach Breast Accomplishment Lv.3
Reach Clit Accomplishment Lv.3
Reach Vagina Accomplishment Lv.3
Kisses x1000
Reach Orgasm x4
Reach Orgasm x8
Obtain Black Cat Cape Doll
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
Reach Orgasm x2
First Time