King of the Vampires and Lord of the Undead, he has fought many battles against Odin. Brahms holds the spirit of Silmeria, one of the three Goddesses of Fate hostage, but his sense of honor prevents him from ever harming her. His power exceeds that of a god and a battle between him and the gods has been suspended for the time being. Brahms becomes a playable character in the Seraphic Gate. The requirements for this are two Flame Jewels, the first to unlock Brahms, the second is needed to acquire his ultimate weapon. Brahams, however, does not join your party outright, you must first defeat him in battle.
Brahms played a major roll raging a war verses Odin for an unknown amount time during which Hrist was tasked with handling him. But this all happened before the Valkyrie Profile story we play, so it's all unknown. Other then being able to recruit him in the Seraphic Gate, you only have a chance to encounter him two times during the normal game. First you need to visit him at his castle in order to help trigger Ending A during chapter four. You have a choice to fight him or not to, choosing not to fight him will bring you one step closer to achieving Ending A. On the other hand, choosing to fight Brahms will make it more difficult to get Ending A. This is also not a good idea because you are just making things harder for yourself and you have almost zero chance to defeat Brahms. And even if you somehow manage to win, there is no reward.
At this point, the next time you encounter Brahams is at the end of the game, during Ending A when Hrist goes to challenge Brhams at his castle in an attempt to free her sister, Silmeria. Ultimately, with Brahms assistance, Hrist is defeated and Lenneth's spirit is returned to her vessel. The last time you see Brahms is after the Ending A credits. Brahms will appear, he says that: Odin has fallen, and Valkyrie has become Lord of Creation. The Promised Land is born. The world is once again reborn and all the Fruits of Creation are ripe with life renewed. The forces of Chaos that rule all are once again set into motion. He laughs saying that he has 1/3rd of the Lord of Creation in the palm of his hand. But the mistress of Niflehiem, Hel, shall not remain silent. And that the man of Midgard (Lezard Valeth) concerns him. He finishes saying... Very well, let us go to the dark abyss eh, Simeria?