No one gets drunk from liquor chocolates. You need to eat like 700 grams of the stuff to get even a little bit tipsy, and that also depends on the alcohol percentage content of the stuff.
By then you'd already kill yourself with the sugar intake
Just from some quick research, the novels appear to have nothing to do with what happens in the manga, which is the source material. It sounds like it's all alt-universe or side-story stuff.
Pretty sure we're not meant to know what they actually did to him, just that they all (including Marika Tachibana, who has never seemed like the type to be tight-lipped about getting frisky with Raku) want to forget and never speak of this event ever again, so I don't think we can even safely say it was what a lot of other comments are outright saying, unless she really does feel extreme shame at forcing herself on him, which almost feels out of character considering all the other shit she forces onto his ass because of her psycho behavior, which was totally in full creeper bloom up until the drunk sequence. God, she makes my skin crawl.