Though it isn't domestic violence in the traditional sense, there is a gang of traffickers shown to abuse their female slaves with adjacent language/injuries. (Trigun Volume 2, Chapter 5)
Dependent on reader viewpoint. An antagonist who routinely uses his abilities to take control of the bodies of others in order to harm, torture, or kill is revealed to have been a victim of childhood sexual abuse. His actions throughout the series are not abuse, but they are assault of a very invasive kind.
Also, Vash's drink is roofied in order to make him fall asleep, but nothing happens to him (or is planned to happen) while he's unconscious. (Trigun: Volume 1 - Chapter 5)
Vash is drugged and left unconscious in the first volume of the original Trigun manga (Volume 1 Chapter 5). Multiple characters are intentionally paralyzed via insect in Volume 11 Chapter 4.
In one chapter an adult gropes a 12 year old girl. We do not see this happen however it is discussed and we see the man trying to come after her for kicking him.
There is a graphic rape scene in a flashback (Trigun Maximum: Volume 12 - Chapter 9), as well as multiple innuendos/catcallings by background characters throughout the series. A gang of traffickers is depicted with sex slaves, but nothing sexual happens to them on screen, and they are soon freed. (Trigun Volume 2, Chapter 5)
One girl mentions a "lolicon" and briefly describes being molested. (Trigun Maximum: Volume 1 - Chapter 1)
Vash gets his hair cut/beard shaved (Trigun Maximum Volume 1, Chapter 2). There are many graphic arm-related injuries, cuts being only a small portion, but most are not intended as self-harm.
There is a crowd crushing scene inside a truck. (Trigun Maximum: Volume 2 - Chapter 1) Also, multiple characters are choked/strangled or held in a chokehold.
Wolfwood will spend a lot of the story getting his bones broken in fights throughout the series, though he will recover from these injuries easily. Razlo suffers intense bone trauma in Volume 10.
A gun barrel is shoved into a villain's eye socket. (Trigun: Volume 2 - Chapter 3). An insect crawls into an eye socket (Trigun Maximum: Volume 4 - Chap 3).
Minors are not sexualized or objectified for the audience's gaze, but a flashback shows a minor being assaulted in a graphic scene (volume 12-chapter 9).
Not a toy necessarily, but a child's similarly-cherished map gets crumpled and stomped on by adults. They're stopped before it's completely ruined, however. (Trigun: Volume 1 - Chapter 9)
In a flashback, Vash and Knives both briefly follow what turns out to be the ghost of a dead child, however it is not seen again. (Trigun Maximum: Volume 7 - Chapter 1)
Not possessed by ghosts, but many characters fighting Legato get involuntarily controlled by his powers while still conscious and forced to act against their will.
A young girl is described as growing multiple tumors and dying. She is shown in detail suffering the effects of treatment. (Trigun Maximum: Volume 7 - Chapter 1)
Great swaths of the cast are both mentally ill and violent, either by choice or by necessity. In specific, Livio's alter Razlo is shown to relish violence, and commits violence towards an animal in a Volume 9 flashback. The relationship between the two is largely symbiotic, though contentious at times.
A character with D.I.D. is present from Volume 7 onwards. An alter is depicted as excessively violent and harms an animal in a flashback. The author does not appear to have held a solid understanding of the mechanisms of the disorder, but does not depict either persona as explicitly villainous or evil.
Along with Vash and Knives' childhood trauma in Volume 7, Vash is shown to be under severe mental distress in Volume 5. Meryl's PTSD is triggered in Volume 6.
not explicitly but the main character shows passive suicidal ideation on multiple ocasions (including but not limited to telling another character he can kill him #7 vol4) as well as holding the sentiment he should never have been born
A character commits suicide by jumping (Trigun Volume 2, Chapter 8). There are two different methods of attempted suicide by the same character in a flashback. (Trigun Maximum: Volume 7 - Chapter 2)
Vash, Knives, and Tesla are all shown as infants at some point in their backstories. Wolfwood cares for an infant in his spinoff chapter. Occasionally babies are present as background characters. Dependent plants are often depicted with infant bodies/body parts attached to their adult ones, though these are a part of a singular entity and not their own individuals.
A plant gives birth to a fully-grown man. It is only a few panels, but the birth, as well as the pregnant belly is shown in explicit detail. (Trigun Volume 2, Chapter 8)
Other plants are implied to have given birth, but the delivery is not shown, only the blood.
A character mentions their "uncle was into sodomy" in regards to their abuse, though it's immediately revealed in their thoughts to be a lie. (Trigun: Volume 1 - Chapter 4)
In the sense that several major characters have no permanent address and travel throughout the story, but it is typically not a theme of the narrative or explored.
Many cars and motorcycles crash, and there is a minor sub-plot based heavily on the plan to crash the in-universe equivalent of a giant train/car carrying hundreds of people. (Trigun: Volume 1 - Chapters 4-9)