Many animals die across the series, including a wolf in the flashback of Team Winter, and two well-known dogs/wolves that are present in much of the series die through fire later on.
There is an attempted rape scene in the end to the beginning of ch 78 ("Thirst") to ch 79 ("Protect"). There is also an attempted sexual assault against a character not long after Team Spring is first introduced.
In the flashback arc for Team Summer A, many different animals die as one of the same characters who raised them takes it upon himself to kill them all so that they cannot exist wild in the future. This includes a bear, a tiger, fish, and other animals.
Team Summer A were not brought up in normal homes, and were instead raised by all male teachers who would randomly jump them, put them in headlocks, etc. One teacher punched a teen boy in the stomach. The same teen was also put into a vat of meat that contained the remains of another character he had known before. These same adults also force them to survive until only 7 are left--the rest die in accidents or natural disasters without any help from the adults. Some characters are even trapped by the adults.
A character at the end of the Ryugu Shelter arc dies by cutting his throat in order to keep the infectious virus in his body from spreading out into the world. This happens mostly offscreen, but a blood splatter and his skeleton makes it obvious what happened.
Although not necessarily suicide, another character does cut a rope that causes his own death in order to save another.
Most of the characters are teenagers when they first arrive in the future. Multiple teens die in Team Winter, and many more die throughout the course of Team Summer A's flashbacks, since only 7 out of around 100 original kids/teens were allowed to be chosen.
A character who becomes internally infested by insect larva eating him from the inside sacrifices himself with the last of his mental control by burning his body with a lighter.
A group of characters have PTSD and though not all of them are violent, one in particular goes into moments of rage and anger that lead to him harming others.
At the beginning, Team Summer B comes in contact with a massive amount of cockroaches. Later, when Team Spring is first shown, they are on an island filled with giant insects. One character even has a giant bug's eggs inserted into his body. The larva later hatch from inside of him after eating his insides.
Guns are shown in the Team Summer A flashback. A character is shot and killed with a gun. Team Summer A is the only team to start with guns and know how to wield them.
A minor character dies after being locked in a place filled with water. It is not graphic. Another character jumps into the water for a long time and is "saved" by someone else who believes he was trying to kill himself, or almost be eaten by a sea creature.
Natsu appears to have bad anxiety that sometimes leads to her breathing heavily or overwhelmed, but these are normally resolved. Other characters are occasionally placed under a lot of stress that triggers a similar fight-or-flight response due to fear.