Hello, I am trying to remember a manga which was adapted into

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Hello, I am trying to remember a manga which was adapted into an anime around a decade or so ago. I never read it or watched it.

I remember that it had four male characters who adventured together, The one character was a blond kid. I'm pretty sure they all had guns - at least the one edgy guy with long burgundy/dark red hair, a headband and a tattoo did. I think it was a loose adaptation of Romance of the Three Kingdoms, written by a female author though I'm not sure of that.

Unfortunately that's all I can recall.