No. There is a few allegations about a character (Mayoi Ayase) being pedophilic, but if you dig deeper into his character it's shown that he has intrusive thoughts about more cutesy things, like his unit mate Aira and his friend Shinobu. In reality he wants to take care of them in a motherly way. But due to some things, those thoughts will turn twisted and he'll blurt them out. He's said it himself that he hates those thoughts too.
Kind of?? Shu was previously abusive towards Nazuna and Mika, but they have since collectively moved past and resolved this. Nagisa is implied to be a human trafficking victim, and he frequently talks highly of his late "adoptive father" who isolated him for a majority of his childhood, among other vague and dubious things.
In the main story in the second chapter I believe, Mayoi watches Aira from the side of his bed. Mayoi has also spied on characters from the ceilings too as a Yumenosaki Mystery and also in the beginning of the main story. Where he was hidden in the vents due to his anxiety to show up in person. Also a few other times with Madara and the rest of ALKALOID.
technically yes it is said in the story "Checkmate" (epilogue 1) that Leo Tsukinaga had bit his hands till they bled because he was struggling to even compose anything ( i don't believe it was shown on screen though)
It's talked about how the Aoi twins' father is very abusive towards them. Arashi's family was trash, so is Eichi's, Mikejima got disowned and Kanata's parents convinced him he was a god therefore he wasn't treated like a person. There's much more than just those six characters though.
During Checkmate, Leo describes being beaten to the point of having a broken arm. Kuro gets beaten by bullies in Meteor Impact. This is just a thing that happens all the time.
While more explicit references are limited to the Meteor Impact event story, Kanata Shinkai was raised in a cult which would follow cannibalistic traditions in times of disaster. These traditions are explicitly described within the event story, and directly affect Kanata's life at that point of the story, as well as his morals and self-perception during the whole series.
There are also light-hearted gags about cannibalism including Niki Shiina when he is particularly hungry.
One particular scene that references Niki Shiina's father's past during the !! Main Story may be seen as having cannibalistic implications, but it's currently just fan speculation.
not really *burried*, but mika once noticed that ritsu didn't move, so he carried him to the es garden and started digging the ground to bury, but the ritsu woke up and said it was some kind of a joke
In "Checkmate", a character breaks their arm. Another character gives a pretty graphic description of the event in the chapter titled "A Solitary Throne - 7". There's also a more minor example with Tatsumi having broken his leg in the past.
There's a whole cult with cannibalistic sacrifice, Hinata tried to kill himself as a sacrifice for his brother's wellbeing, Rinne and Hiiro have a non-death sacrifice thing
koga used to call arashi "okama bastard" but then he change it to "ari" bc he doesnt like arashi's expression everytime he calls her that and subaru calls arashi "okama". okama means a gay man, in the context of japanese culture, especially to a person who is effeminate and cross dressing
Eichi Tenshouin has a terminal illness. Throughout the story he is often hospitalized due to his condition, and he is very aware of his life expectancy, his relationship with mortality being a driving force behind many of his actions. Due to the nature of the series as an idol franchise he is extremely unlikely to actually die, and is shown to have supportive friends and lead a fulfilling life.
Eichi Tenshouin is often hospitalized due to terminal illness. There are many instances of hospitals being brought up, or characters visiting hospitals for one reason or another. Instances include the beginning of Checkmate, and Tatsumi Kazehaya's mentions of being hospitalized in the past.
In one story in ! (Victoria), one character claims that Shu has "Dissassociative Identity Disorder", but considering Shu's behaviour throughout the series, this is incorrect, as he does not meet the criteria for diagnosis. This seems to be a misinterpretation of the condition on the writer's behalf.
There are quite a few Autistic-coded characters (Nagisa, Sora, Kanata etc). Some of these characters are insulted or bullied for showing autistic traits (strange speech, unusual interests etc)
No main characters actually die by suicide. However, many students committed suicide during the War. Hinata Aoi attempted suicide during the story and it was mentioned that Kanata Shinkai may have, but neither of them died from it.
In the older stories, Subaru and Koga referred to Arashi as “Okama”. Okama can either be a term to describe an effeminate man or be the equivalent of the derogatory term used to call homosexuals.