Harrow's parents tie a noose for her to use when they commit suicide, expecting her to do the same. She thinks of them as kind, but we later learn (in Harrow the Ninth) they were neglectful.
Gideon and Harrow, yes. Harrow is framed by Gideon as more of a nemesis or an enemy on equal footing, which she is not. Harrow has much more power in their dynamic, instigated all mentioned fights, and kept Gideon against her will on their planet (from enlisting to join their army) where she is a social pariah. Harrow does have character growth and much of the more violent abuse she is blamed for is actually another character's (Crux's) doing, unbeknownst to Gideon.
This is probably getting "Yes"s because, before the characters develop a very VERY subtle romance, they got into vicious fights throughout their childhood and adolescence.
Harrow is abusive to Gideon due to her wider frustrations, which appears to be from a combination overburdening a child to a degree that would would be seen as abusive (see "is a child abused by their parents")
In a very minor way. A character consumes part of another character's hair and a thumbnail, and bites their hand. It's a very minor thing and is part of their magic
There's a scene in the first chapter where a character loses multiple teeth during a fight. They are later put back into place with magic, but it mentions that the reapplication was rough and still causes her pain weeks later.
There is a bath-like scene in a pool between leads at one point but they are clothed, and Gideon describes taking a bath and using a high tech shower-like device but nothing is described in much detail
A prison has its location mentioned and some communication with it occours. The titular characters is an indentured servant kept in poor conditions in a cell, and frequently punished for trying to escape.
Two major characters are scientists who partially function as medics, and they have some medical equipment, apparently including IVs, though no space that would consitute a medical facility.
There is a morgue.
The final scene in the Eplilogue takes place in a hospital.
Harrow repeatedly harms herself but only to use her blood for necromancy and to use her blood as ink. However, her blasé nature about it makes Gideon uncomfortable at times.
Debatable. Harrow has schizophrenia, but is not violent because of her mental illness and, as far I remember, is only physical in self defense and/or during typical fantasy fights.
CharacterA attempted suicided but decided she wanted to live. Immediately after, her parents do commit suicide. At the end of the book, another character sacrifices herself so characterA can live.
One of the characters rarely turns up for meals and sees food as a necessity, rather than a thing to enjoy. This is very subtle and not really openly pointed out in the narrative.
Both Gideon and Harrow have had terrible childhoods and are traumatised by it. Throughout the novel, as more characters die, the remaining characters become more and more traumatised by the events. The ending leaves Harrow extremely traumatised and the sequel deals nearly entirely in her PTSD from the events of this book.
Several characters use profanity including the lead Gideon who does so frequently. But it is not especially vulgar and mostly as sort of a tonal gag in the writing
A character has a complicated vaguely romantic or adjacent association with another with a large age gap.
A character has an intense obvious crush on their seven year older friend, since at least the age of 13, aged 20 and 27 in the book. These feelings are taken as serious feelings with tact and sympathy, despite the romantic portion not being recipicated. The younger character accepts this, particularly as they are aware that they are too young for the older one to even concieve of being interested being in them.
No real world religions are discussed, but the characters all belong to an empire called the nine houses, whose ruler is their god. The main character belongs to the ninth house, also known as "Shadow cultists" due to their unique religious focus within the empire.