The game over sequences could be considered a form of torture as it is a punishment for failing the level. The "Farewell" level could also be interpreted as such.
The son seemingly forgives/ is neutral towards his father but we never really see his POV. He is very submissive to his father and never acts against him, even if he makes him do something morally bad. The game does not take this very seriously and it is not portrayed in an especially realistic way but it can still be triggering especially given his lack of agency.
It might appear that people are crushed in the katamari but they are not. There are scenes (the queens diary) where the protagonist gets buried under big piles of objects for comedic effect and he is not hurt.
In the penultimate level, a robot character with human sentience/intelligence is basically dismembered by the player. Not graphic but can be upsetting.
Worthy of note: a character worries about what another character will do to them but they are ignored and end up being right. There is manipulation from the main characters father.
Not intentionally, the parent is knocked out and in a coma but the child is stressed at their father not being there for them. They create a replacement parent figure and the mother is still there. The father wakes up in the end.
The premise of the game involves people being stuck to a large ball. Also The King says "We'll hold it down, you hurry and clean it up" in reference to a person.
There is an underwater level where people can fall into the water but they do not drown. The introduction to the level involves someone struggling to talk/ breathe underwater.
A character has an implied anxiety attack in a cutscene after the level "Wake up the king". This character is overall very anxious and has several moments where they are paranoid.
During the game over scenes there is bullying and physical abuse. The penultimate level involves someone bullying/ taunting another character as they physically harm them. In the post game, a character is threatened with physical harm many times.
Surprisingly yes despite the light hearted tone of the series. They come back, but the scene is pretty sad. It's worth noting that the player is basically forced to kill them.