Some authors really sucks at starting a series.
They have a story in mind but in order to write it they have to come up with a situation in which the two girls meet and start their relationship, but the premise of the story they have in mind is so out of the ordinary that any situation will be absurd and irrealistic but it will be forced anyway in order to start the story.
It was the case with ShuuKura and it is the case with クラスの姫は私のわんこ.
"I saw you didn't let your friend copy your homeworks but you helped her to do them herself so become my master and treat me like a pet" doesn't make any sense.
And the answer to such a thing would be "are you ok in the head?" and not "why me?".
"Because I think you're fit to do it but if you don't want I'll just ask a random guy" is another piece in a discussion that makes you wonder what the hell you are reading.
The pet play itself doesn't have a solid ground even after you read the characters' background, both for the pet that wanted to be treated like a pet because all her life people told her how cute she is and for the MC that turns into a beast out of nowhere because her sister doesn't spend time with her anymore, but in the end it remains just a fetish play they do when they are alone like if it was simply sex, and for the rest of the story they're just a normal couple.
The pet play moments are weird but everything else was very good, I feel like Inukai Anzu is getting better volume after volume. Speaking of which, how did she get so many volumes and series one after the other? She's getting more prolific than Mikami Teren in his golden age.
Anyway, I hope a second volume will be announced because there's still a lot more to elaborate with both the friend and the little sister.