By searching for "most influential deaths in anime" and "most impactful anime deaths", I have came up with the following relevant page: https://www.cbr.com/most-iconic-anime-deaths/ and the list:

1. Mami Tomoe from Puella Magi Madoka Magica: Her death set the tone for the rest of the series, revealing that it was not the light-hearted magical girl anime that it initially seemed to be.

2. Caesar Zeppeli from JoJo's Bizarre Adventure: Battle Tendency: Caesar's heroic death, where he managed to snatch the antidote that Joseph Joestar needed before succumbing to his wounds, is one of the most dramatic scenes in the franchise.

3. Spike Spiegel from Cowboy Bebop: Spike's death, where he delivers his famous "bang" line before collapsing, has been a contentious decision but is also one that has been immortalized in anime culture.

4. Kamina from Tengen Toppa Gurren Lagann: Kamina's death was unexpected, but it was pivotal for the development of Simon, the anime's protagonist. Kamina gets back up from the brink of death to invigorate Simon one last time and help defeat the Beastmen.

5. Jonathan Joestar from JoJo's Bizarre Adventure: Phantom Blood: Jonathan's death, where he holds his adopted brother's severed vampiric head while on a sinking ship, is one of the most famous early deaths in the franchise. He took Dio down with him to protect others, reflecting his noble and principled nature.

6. Zabuza & Haku from Naruto: The first on-screen deaths in the original Naruto series, their demise humanized them as ordinary ninja who were just doing what they had to for survival.

7. Jiraiya from Naruto Shippuden: Despite knowing the risks, Jiraiya bravely took on the important mission of investigating the Akatsuki and Pain on his own. His death was both shocking and devastating, but he made sure to alert the village leaders on how to defeat Pain with his dying message.

8. Portgas D. Ace from One Piece: Ace died while protecting his brother Luffy during the Marineford Arc. A well-timed insult from Admiral Akainu lured Ace back to protect Whitebeard's honor, but Ace was overpowered and acted as a shield to take the killing blow meant for Luffy.

9. Maes Hughes from Fullmetal Alchemist: Brotherhood: Hughes was killed by Envy after discovering a deep government conspiracy. Envy assumed the appearance of Hughes's beloved wife before shooting him dead, making his death scene particularly heart-wrenching

10. Roy Focker from Super Dimension Fortress Macross: Roy suffered fatal injuries during a battle but chose not to go to a hospital. Instead, he accepted his fate and died from blood loss while playing a classical guitar.

This list has been compiled based on a single source found by an internet search, in other words, from an opinion of a single person. Be advised that different sources might provide different ranking or even different criteria by which to include certain event on the list. 

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