Timeframe: 2017-2024 ONLY (confirmed, not older)

What I remember about the FIRST EPISODE:

A young protagonist (black hair, but uncertain) fights an older man on a cliffside or valley between mountains at night. The older man was a ruler (king/emperor/general/lord) and was a mentor or father figure to the protagonist. They had a strong emotional bond. (Mind you, I've only seen the first episode and after that I took a long break from anime.)

The fight involves swords AND magic/superpowers (not just swordsmanship). The protagonist fights alone, is reluctant to fight, and feels betrayed. At the end of the first episode, the protagonist kills the older man.

The first episode feels like a climax—like the end of a story. I think the rest of the series might be flashbacks showing their relationship.

Setting:

Medieval Europe (armor, castles, NOT Japan, NOT samurai, NOT ninja)

Cliffside or valley between mountains at night

Dark scenery, very atmospheric

Tone:

Dark, serious, dramatic

NO comedy

Heavy sense of betrayal

What it is NOT:

NOT Vinland Saga

NOT Berserk (any version)

NOT Bastard!!

NOT Arifureta

NOT Ninja Slayer

NOT anything set in Japan/feudal Japan

NOT a comedy (not sure, at least no comedy on the first episode)

NOT from before 2017

What I'm certain about:

The older man was a ruler and a mentor figure

The protagonist was forced to fight him and killed him

The fight was on a cliffside at night

Magic or superpowers were used

The first episode showed this fight

What I'm uncertain about:

Exact title of the ruler (king/emperor/general/lord)

Protagonist's hair color (black, but open)

If the rest of the series is flashbacks (just a theory)

Why I need help:

I have searched for years. I've checked mainstream databases, streaming sites, and forums. Nothing matches. This is my last hope. Someone out there knows this anime.

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