No, but the main leads want to get married although his father and her mother want to marry each other and are not the biological parent of the other lead. (I note this because the leads think they cant get married because this would make them "siblings")
SPOILERS the main female lead dies as a teen (her age isnt specified, but she is not an adult) in a parallel universe while shifting which causes her body in Universe 0 to be in a coma state, she then suddenly dies in Universe 0 as well
There is a partially nude scene when the male lead shifts to a parallel universe and finds himself in bed (naked) with a woman (also naked), he doesnt know this woman and he is clearly uncomfortable as he covers himself up further. We dont see any genitals, but when the woman turns to look at the male lead, we see part of her breasts
The male lead is seen sometimes "talking to himself" (he is talking to someone other people cant see), people move away from him and are shown to be weirded out- note, this may also be because he is holding beer in one of those scenes, so he may appear to be drunk to others
Sort of? The male and female lead's parents get divorced and they both end up having to choose between the parents. The female lead seems unbothered by her dad's absence until she sees him again after the divorce many years later, her mother is present though somewhat emotionally unavailable, and the male lead's parents are both present in some capacity, though also divorced.
One of the main leads receives a childs toy gun which he aims at his pet dog in a joking manner (this was very upsetting to me as he is seen shooting rocks from this same gun at leaves which are shown to have holes in them as a consequence), however the gun is immediately taken from his hands and his grandfather reprimands him for aiming it at an animal, his grandmother gives him a note saying to not aim it at any people or animals
There is a scene at the beginning where there are two characters scuba diving underwater, but there are no details in the water except bubbles and they seem to be there on purpose/or as an allegory, as they are not being held and are breathing fine through masks
SPOILERS there is a scene where the main lead shifts because he wants to see his pet dog who has passed away in his universe; he does see her, except in that universe his grandfather has died. They hold a funeral in the house and the grandfather's body is covered in towels/blankets
There is at least one scene where the male lead has many beer cans around him in his house, and another scene where he is drunk in the street talking to someone
SPOILERS, the female lead becomes a ghost and the male lead goes to see her a few times without her knowing he's looking, but it's unclear if this is definitely true because there are other scenes where she knows hes there without looking at him, but it may still be uncomfortable for some viewers
SPOILERS, the female lead dies in a parallel universe, her consciousness is unable to find her body so she ends up being a ghost in her original universe
Yes, as for most of the answers here, SPOILER WARNING, the movie is about parallel universes and shifting between them, the female lead ends up in a state of brain death due to an accident while her consciousness was in a parallel universe
The main characters get into a chamber together, but the chamber is see-through and they dont seem uncomfortable about it. The male lead makes a comment apologising that he's so close to the female lead because there isn't much space