One of the bosses is a chef who pickled (and likely cooked, served, and ate) other sentient bugs, though this can only be seen by accessing a secret room.
Very late into the game, an area has collapsed rocks where NPCs used to be. No bodies are seen, but the area is inaccessible and it's implied that a character may have been crushed under the rubble.
Minorly discussed. Player character mentions that she has outlived the natural lives of many previous partners due to her unusually long lifespan in an optional journal entry.
Discussed and subverted. A character is shown to be severely ill, and expects to die from his illness. He is later shown to have been crushed to death by falling debris, partly due to being too sick to move.
An infant(?) root creature, which was implanted into the player character for the purposes of incubation, acts as a curse on the character, and can be removed/destroyed through a medical procedure. The root then changes into an upgrade that the player character keeps.
Implied. During a memory sequence, we are shown that the player character has very unclear memories of her mother, suggesting abandonment. This is further discussed in the previous game: Hollow Knight
There is a child character who tries to lick/taste the main character, and gets slapped one time. The child is unharmed and continues being friendly with the main character.
Grand Mother Silk is said to have been very controlling of her children, as well as attacking the player character whom she seeks as a surogate daughter.
Spiders are a central theme and spider-like creatures appear throughout. However, they are highly stylised and I know of at least one arachnophobe who has played it without trouble.
There is a semi-optional quest involving getting a bunch of rare food items for a respected gourmand, and they eat it audibly and noisily as the screen goes dark. Noises are not pleasant, but turning the volume down for a few seconds avoids the issue. There is also a collectible music disk item that plays the crunching and squelching sounds of a bug getting surgery done on them, though it is entirely optional to both obtain and play.
It is a major theme and there is a lot of religious imagery/discussion throughout. The actual religion is fictional but bears some superficial similarities to Christianity.
Some people misread a specific character's backstory as being incestuous, though they and their partner were just born at the same time and are considered to be soulmates. A few poor translations make a similar mistake.
During one section the player character's cloak is stolen and she appears "nude". However, she just looks like a stick figure, and it is not in any way presented as sexual.