*I'll be using the translations of the link
here (the post above yours). Just the most important ones until the third volume.
- Volume 1:
Honda Tadakatsu/
Kazuno/
Matsudaira Motonobu = They all died to pass the message about the Apocalypse to the world. Because ether vein(s?) in Mikawa got out of control, Mikawa "exploded" and that's it. In the fifth episode you'll understand how awesome was this.
- Volume 2:
Nobody important died. Well, there is a character that "dies", but it's not important.
- Volume 3:
Before writing, I'll say that the deaths here are one of the main reasons that a lot of fans (including myself) want to see
at least a third season of Horizon. I would say that it's not the best thing to know about this now, but...
1)
Anne d'Autriche (
Anne of Austria) = In the world of Horizon, Anne was the little sister of the Louis XIV. She died because she wanted to protect the people she loved (of Hexagon Francaise) and the new generation (Musashi). This happened because the enemy, the Hashiba forces from P.A.ODA (Oda Nobunaga is the leader) used a "bomb of ether".
2)
Matsunaga Hisahide = The senpai of Nobunaga in "destroying", died to allow Musashi to go on. He destroyed the ship he was in and that's it. He did that because he found two idiots that he could trust the world (Nobunaga as the one who destroys, and Toori as the one who builds).
3)
Minamoto Yoshitsune = She already appeared in the anime (first character to appear). She died? because of the same "bomb of ether". It's not certain if she really died (I don't want to believe in this), so I won't comment much on this.
4)
Satomi Yoshiyori (Second) = He died in the place of the Marga Naruze: First of all you have to know that Marga has the name of Naruse Masayoshi, a person who died in the
battle of Mikatagahara. And they were "remaking" this battle, so the enemies requested that Marga should die. What happened in the third volume was that Yoshiyori took this name and died in her place (one of the best scenes in Horizon until now).He did that entrusting everything about Satomi to Toori and to prevent other tragic deaths happening from now on.