Acceptance is a hidden stat that represents how accepting Eric(a) is of their feminizing changes. It affects choices, descriptions in the mirror, and even GUI appearances, turning pinker the more acceptance points acquired. These GUI changes, along with corresponding shifts in Eric(a)s attitude towards his changes, occur at 5, 10, and 15 points.
Methods
Though there is no current use for Acceptance points aside from aesthetics and word changes across various scenes (and the description of the mirror), here are the choices for gaining acceptance to Eric(a)'s changes:
Nature Magic: Intermediate Course: After accepting Tilia's offer to help your magic and breasts grow for a second time, once you leave her tree choosing that Maybe? and then choosing I kinda like it.
TRAPped Again: After defeating Gloomwing, choosing "Maybe..." to Isabelle's question will count towards acceptance.
Counting On Your Cleavage: During Tilia's "challenge," choosing "Having boobs isn't so bad" will count towards acceptance, and will result in automatically losing the challenge.
Gracious in Defeat: After losing Tilia's "challenge," you can choose not to be upset over gaining a vagina, which grants you one more Acceptance point.
Cuteness Overload: After defeating 4 or more Magicos, talking to Isabelle will make her talk about Eric(a)'s changes, particularly about how cute they're becoming. Agreeing will count towards acceptance.
Go After Her: During the trip to Earth if you choose to immediately go help your companion, a point of acceptance will be gained. Choosing any of the other options and delaying will not gain acceptance, even if you do eventually go to help.
An Imaginary Orgy: Asking Allura to reverse the changes will cause her to give a hypothetical scenario where transformed women would get into orgies. If Eric(a) agrees that that might happen to them, it counts towards acceptance.
The Phantom Pantsu: Picking up the See-through Underwear during the fourth dream of the Wendy Dream Meetings counts towards acceptance. Note that the player will only have the choice to pick them up if they have Panty-Wearer Transformation, and will automatically pick them up if they have the second stage.
A Date with Rosa Palms: Masturbating in the blue dorm's bathroom while under the Cutie Magic Transformation and choosing "Explore more" nets a point toward the end.
Leg treatment at Watanabe Spa: Depending on your choices in this section of the Watanabe Inn dialogue tree, Eric(a) may leave with an additional Acceptance point as well as the Swimmer Legs Transformation. In the female version of this scene, choosing "Nope" when Eric(a) ponders if he really wants his dick restored counts. In the male version, allowing the leg treatment without protest to proceed counts.
Like a Magical Girl (Natalie-Route Only): Have sex with Natalie while under the Cutie Magic Transformation.This can be performed twice.
Yoshida Appreciation Day (Natalie-Route Only): If you speak to Yoshida during her recruitment efforts while in Succubus form, you'll have the option to slap dat ass. Doing so leads Eric(a) to appreciate the things one can get away with when an absurdly sexy girl.