Below is a list of people who've died and a reasoning of their death.
3rd Hokage (Sarutobi)
· Killed by: Himself
· Reasoning: Sarutobi used a forbidden jutsu in an effort to kill Orochimaru, when the jutsu was completed his body was sacrificed to the God of Death.
4th Hokage (Yodaime)
· Killed by: Himself
· Reasoning: Yondaime used a forbidden jutsu to seal the powers of the Kyubi into Naruto. When this jutsu was finished his body wa sacrificed to the God of Death.
4th Kazekage (Gaara's Father)
· Killed by: Orochimaru
· Reasoning: Orochimaru assassinated Gaara's father so he could attend the Chunnin exam disguised as the Kazekage.
Asuma
· Killed by: Hidan
· Reasoning: Asuma was caught in HidanĂ¢€™s jutsu, a technique which, through the victims blood, forms a physical connection between the two ninja. While this technique was active, Hidan was able to stab and burn himself and the damage was transferred to Asuma.
Chiyo-baa-sama
· Killed by: Self
· Reasoning: Uses a special Jutsu to revive Gaara after he his killed by the Akatsuki group, to use the Jutsu however, she had to give up her own life in exchange.
Fuhma Arashi
· Killed by: Falling building
· Reasoning: After being twisted and mutilated by Orochimaru's experiments he was left to defend one of Orochimaru's hide outs. There he battled Naruto, Sakura, Jiraiya and Sasame and during the fight he regained his right mind and allowed himself to be crushed to death when the building collapsed during the fight.
Dosu
· Killed by: Gaara
· Reasoning: Attempted to kill Gaara during the Chuunin exam. He failed and as a result was killed by Gaara.
Gaara of the Desert
· Killed by: Akatsuki (Note: Gaara was later brought back to life by Chiyo·baa·sama)
· Reasoning: Killed as the result of an Akatsuki Jutsu to extract the spirit of Shukaku from Gaara's body.
Gaara's Mother
· Killed by: Birthgiving
· Reasoning: When giving birth to Gaara, the spirit within Gaara was too strong and it killed her.
Gatou
· Killed by: Zabuza
· Reasoning: Gatou betrayed Zabuza. Despite the fact that Zabuza was badly punctured from spears and other weapons; he was still able to kill Gatou with a knife he held by his jaws.
Gatou's Men
· Killed by: Zabuza
· Reasoning: As Zabuza made his way towards Gatou, an army of men was in front of him. Zabuza charged forward and killed all of them.
Gekkou Hayate
· Killed by: Baki
· Reasoning: Gekkou found out about the secret plans plotted against Konoha while Kabuto and Baki were discussing it. Baki killed Gekkou after he failed his jutsu.
Haku
· Killed by: Kakashi
· Reasoning: Kakashi set up his Chidori in an attempt to kill Zabuza. Haku jumped in the way and was killed.
Henchman
· Killed By: Team Kakashi and Team Gai
· Reason: Itachi and Kisame used these two henchman to act through using their astral projection and when the two teams killed them found out they were just fakes.
Hyuuga Hizashi
· Killed by: Sacrifice
· Reasoning: Hizashi chose to sacrifice himself in the place of his brother.
Iruka's Parents
· Killed by: Kyubi
· Reasoning: Kyubi attacked the village and Iruka's parents were killed during the havoc.
Jiroubu
· Killed by: Chouji
· Reasoning: Jiroubu was out to stop Chouji from getting to Sasuke. Chouji ate his pills and tripled his strength to kill Jiroubu.
Kaguya Kimimaro
· Killed by: Gaara/Disease
· Reasoning: Even though his body was under attack from a fatal disease, Kimimaro went to ensure Sasuke's safe delivery to Orochimaru. During Kimimaro's fight with Rock Lee, Gaara came and fought Kimimaro until he could no longer resist the disease and died.
Kaiza
· Killed by: Gotah
· Reasoning: Kaiza was killed as an example of what Gotah would do.
Kurosuki Raiga
· Killed by: Self
· Reasoning: After being defeated by Naruto's Rasengan and seeing his partner Ranmaru living happy without him, he gave himself a "funeral" in a massive blast of his own lightning.
Kidomaru
· Killed by: Neji
· Reasoning: Kidomaru was trying to hinder Neji from getting to Sasuke. Neji hit Kidomaru with his tenketsu right in the face and killed him.
Kin
· Killed by: Orochimaru
· Reasoning: Kin was used by Orochimaru as a sacrifice in order to perform a justu.
Rokushou Aoi
· Killed by: Naruto
· Reasoning: He was hired by the Wagarashi Clan to help aid their runner in the Todoroki Shrine Race. During the race, Aoi encountered Idate along with Sakura, Sasuke, and Naruto. In the ensuing battle Aoi was sent off the cliff and fell to his death into the water after being hit by Naruto's Rasengan.
Sakon & Ukon
· Killed by: Kankuro
· Reasoning: They were trying to stop Kiba from retrieving Sasuke. Kankuro came to help Kiba and killed both of them using his puppets Karasu and Kuroari.
Sasori of the Red Sand
· Killed by: Chiyo-baa-sama
· Reasoning: Tried to stop Chiyo and Sakura as they attempted to rescue the kidnapped Gaara and ended up being stabbed to death by two of Chiyo's puppets.
Tayuya
· Killed by: Temari
· Reasoning: She was trying to stop Shikamaru from retrieving Sasuke. Temari came to Shikamaru's aid and killed Tayuya with her summon Kamatari and her Kamaitachi no Jutsu (Cutting Whirlwind Jutsu).
Uchiha Clan Members
· Killed by: Itachi
· Reasoning: Itachi wanted to test out his strength and he killed all the members except Sasuke.
Yashamaru
· Killed by: Gaara
· Reasoning: Yashamaru was Gaara's caretaker. He tried to murder Gaara and he accidentally killed him.
Zaku
· Killed by: Orochimaru
· Reasoning: Zaku was used by Orochimaru as a sacrifice in order to perform a justu.