Definition of Dead
"Dead" in Toshiro's concept was when the chain of fate is broken and the soul departs from its body. It can never return to its previous life, so it is stuck until a soul reaper appears to make a soul burial for it. However, when the soul is out for too long, Hollows would devour the soul, or the soul would become a Hollow itself. Death is like reincarnation in Soul Society as well. If a soul dies in Soul Society, it is reborn in the human world with a new identity. Toshiro knows that the dead could not revive, but what he is witnessing would amuse him for a bit.
"Dead" in Yuzu's vocabulary was when the person can no longer go back to the way he or she once lived. In a dire situation where and when the person could no longer survive under the intense pain, the person gives up and accepts the fact that he or she must stay. Wars, accidents, revenge, hiding vital secrets, murders, and illnesses are the causes for death, and it is added to the causalities for the number of people who are involved in such an event. She has seen death before, and she accepted the fact that it was the person's time. However, she was baffled at this one case.
"Dead" in Heiwa's knowledge was never coming back alive that a person once lived its previous life. She notices signs of the fading life and the cases of each death. Pale skin, dropping temperature, and a slower heart beat are signs that the person is close to death. Science has also proven that the corpse would also have its stored liquid flow out of the bodies, transforming into a foul smell people couldn't stand. Causes of death would involve careful autopsy and observation to figure out whom or what killed the person. Death would be involved a long time illness, but it could be someone who made a grave mistake that stepped over the boundaries.
"Dead" in Natsu's fact was the feeling of dread before something bad was going to happen to the character. Games, movies, and books revealed that one or more of the characters are going to die in the later chapters. It involves heartbreaks, anger toward the villain, or self-defense in battles. It was gruesome, but life continues as the character learns from his mistakes. His father told him that death is part of life, revolving in a circle for their new life in later years. He didn't understand that, but when he saw those ghosts and soul reapers, he understood that death is truly a part of the cycle. He has seen them of how people die, but not in his life that he would be one of them.
"Dead" in Karin's information is based on whether how much intent the person wants to hurt you. Yep. You heard her right. There are two definitions about "dead" in Karin's logic. The original knowledge of death is about having your right to live being stripped away by another person. Now, having a mind of a teenager, death was just a sarcastic way of saying that the person, who made a grave mistake such as hurting a person's feelings, would be tortured for a long time or be in pain through the horrors of an individual or a group in every cynical way. Death through selfish events is the gory, shrieking, horrific scene that no one wanted to see. Playful or teaching-a-lesson death is another event for someone to be reminded or remembered to have manners, and it could also be converted into people's enjoyment to witness their dear friend's hide being wiped on the wooden floor by his dear sister.
Watching Natsu run past all of their comrades like the wind and being followed by his enraged twin gave her lots of laughs as Heiwa screeched at him while trying to trap him in her controlled water. Some of their comrades wondered what happened; others laughed along to see the screwed Natsu running for his dear life. Karin knew that this wasn't serious, but it was to learn a painful lesson to not enter her room unexpected while she was changing.