while the bunnygirl is fine, she's basically average for a stroke concept.... she shows the process works, and is sexy, but the catgirl, so far, is your real primary story telling concept.... yes, hypnosis works on her... but never quite right, and to comic results... even from before she was hypnotized, she had an atypical, comic response [not "ahhh, I'm being held captive!" but "there's my night..."
in other words, the bunnygirl/mad scientist is your straight man, and the cat girl is your bananaman
so what I want to see is;
1) other ways the cat girl can exasperate the scientist, especially with cat like behavior
a) knocking things over or snatching things [usually food] meant for others
b) urine or hairballs anywhere that isn't the litterbox
c) wandering outside ....uh oh! need to hope no one sees or can explain it away
d) comes back with a prize/kill
e) random pouncing "attacks" [sexy attacks]
f) seeming to desperately want something,
f) bathing trouble and/or licking
g) being lazy/cute.... and/or mad scientist wants something, but so lazy-cute, can't bear to enforce it
2) why she became a cat girl and not a bunny girl... at the time, the explanation was "a glitch" - that's a boring answer, but fine at the time
is the base process more complex then he thought, and he'll continue experimenting and getting strange results [harem comedy] ? Does it draw from the person's individual mind, so the results aren't very predictable? Or is the catgirl a unique case for some reason?
3) in cannon, the mad scientist mentioned a hero might try to undo the hypnosis, so you have some potential conflict there. If you want it to be temporary, the hero is the antagonist and follows the rule of 3 [protagonist loses first match to establish threat, ties second match to show growth, and wins 3rd match, triumphing over antagonist]
also, hero as in simply someone realistically heroic, or bond spy, or hero as is super hero/magical girl/sentai
4) alternatively, the hero could become your hero - while it is played for laughs, the mad scientist is randomly grabbing people, regardless of their current lives, and making them permanent sex slaves; arguably murder by ego-death... in the long term, that sort of thing isn't likable
Now that the plot is established, after a rescue you could deal with someone both trying to stop a mad scientist who might have anyone brainwashed while also keeping a sexed up over-obedient pet girl
5) the mad scientist said the brainwashing is permanent.... but what about doing a 2nd brainwashing into being who they were before, with no underlying command to obey?