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