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