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You need to visit the pub in Sylva city, get the quest to start looking for ingredients for the "Mont Blanc" dish, then go to the Myrtle Forest to gather ingredients. After that the dialogue should be able to take you the rest of the way.

My guess is that its based off of  the Endurance Talent. The higher your characters Talent, the more alcohol they can withstand.  Also, if you eat more than one meal in a day your characters can become "Stuffed" which helps prevent passing out from alcohol consumption. Now, I'm not sure EXACTLY how the alcohol system works, in the attached photo my Rosalotta has a Tolerance of "190" based on her endurance stat, but I've never had a character last drinking more than 1 Wet Maria and 1 Hrd Dck in a session, both of which have an alcohol level of 50. The Journal page for Intoxicated also isn't very helpful, unfortunately.

Marie and Ran both should come with alternate versions of their outfits. If you complete Ran's "Too Hot to Handle" sidestory, you get an outfit for her.
ETA: On Dearonnus offical patreon (artist of NBD) they state that 22 total outfits are in the game. Some are color variants of other costumes

2nd ETA/R: Helps the slums people with a hidden character specifically enough times and you'll get an outfit 

Theres a page that gives you the clue, each digit corrosponds to the number of books, their orientation, and color, scattered around the library. ex. Red books that are Vertical. = digit 1. That kind of thing

In the red district, the guy on the bench in the bottom left of the screen was the most recent victim, talk to him and it should progress for you

Just wanted to add to this - Im lvl 44 across all 4 party members, with every heritage unlocked, and killswipe still doesn't activate in the sand caverns, but does activate in ALTOMYSTR and other areas.

One more thing, I think I've beat the game now (or whats out so far)  and I cant view the momma rena scene after giving her the gift. The photo doesnt show up when giving her the gift and when I try to view it in the gallery it still tells me to explore and find the gift.

Tried to load a new save file and use the skip crystal to get back to the kuro area and had the same issue.

repeatable bug, i picked up the slime and flesh pet before re-entering the digivice, the two events seems to freeze the game

Ill start a new game and try to recreate it. Im not sure what initially caused it but i think it may have been playing some events out of order

I am unable to use the digivice for some reason now, as every time I try I'm unable to do anything once inside the digivice. I first encountered this when trying to fight the midboss in the fleshy area.

Go into the game files and delete the already existing save file. Then when you restart the game it will create a new save file that it can access