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Etherian War Champion also known as Mga Maharlikang Nakalaban ng mga Etherian (Nobles fought by the Etherians) is an honorary title given to those who greatly contributed to the fall of Etheria.
Known for her extraordinary powers and abilities, Cassiopea is obviously one of those who championed the war.
Mentioned by Sir Noel on his behance as one of the Champions of the said war.
Being the older sister of Amihan (I), Mine-a without a doubt is alive in that time period. If her sister was given the title it isn't surprising that Mine-a gained the title too especially because she is called as the Warrior Queen of Lireo. In Episode 200 she was regarded by Andora as a mortal enemy of the Etherians along with Cassiopea.
Hagorn aided in defeating the Etherian forces with his strategic ways. A proof that he bears the title is when Avria mentions that she remembers Hagorn as one of the enemies—one of those who participated in the War against Etheria that lead to it's downfall.
The following are only hinted or theorized to be given the title.
Adhara: Adhara was alive during that time and is hinted to be one of those titleholders since she is also called as the Warmonger.
Arvak: Arvak possibly wasn't that greedy for power that time and has contributed to the fall of Etheria.
Raquim: Back in the 2005 series he was one of those who were against Etheria's abusive ways and greatly contributed in saving those who are unable to fight. It isn't impossible that in the 2016 he is also one of those that contributed to the kingdom's demise.
Bartimus: only mentioned in Sir Noel Layon Flores' Behance Account to be canon, but not mentioned if he was part of the war. However, since he (his counterpart) was one of those who revolutionized the war back in 2006, there is a possibility that he is one of the titleholders in this requel.
Ursula: only a mentioned character. It is possible that she also gained the title because she is worthy enough to be chosen as Cassiopea's successor as Queen of Lireo.
Demetria: only a mentioned character she could possibly be a titleholder.
Menno: only a mentioned character, he could still be alive at that time since he was mentioned to have held the Brilyante ng Lupa. He also could possibly be a titleholder as his counterpart was one of those who've led the revolution against the Kingdom of Etheria.
Aegen - This character is not confirmed to have existed in this series yet but are theorized by fans to have been one of those who've led the revolution against Etheria as his counterpart character has back in 2006.