The Pirate King Edgar was killed by an "unnamed pirate," who Brandeau killed in the very same skirmish. This unnamed pirate had the Rune of Punishment, which then went to Brandeau.
This supposedly happened relatively recently from the context of the year 305, when the whole Island Nations War took place. However, we still don't know who it was that killed Edgar, and passed on the rune to Brandeau.
The owner of the Rune of Punishment before Edgar was Rakgi's dad, who went missing 1 or 2 years before Suikoden 4's timeline (Konami has only officially stated "1 or 2 years ago."). Would it be possible that Rakgi's dad was this "unnamed pirate?"
Rakgi's dad left his family because he didn't want the rune to harm them. Besides that, nobody knows where Rakgi's dad may have gone after he left Na-Nal. It is entirely possible that he was killed by some other pirate, but if he had such a powerful rune, it would make sense that he would use it to defend himself.
As the game has demonstrated, the Rune of Punishment doesn't kill it's user upon it's first use all the time. It seems to depend on the degree to which it is used, such as how Glen and the Queen of Obel use it to annihilate entire fleets (resulting in their deaths). We see Brandeau use it to a lesser extent, and he did not die. Thus, it is possible that Rakgi's dad managed to survive for a while, killing pirates (which would be a "good" thing for an ex-fisherman like him to do), and receiving some notoriety.
It's just a hypothesis, but I don't find any evidence that would possibly counter it. I personally like the idea, because it adds a little more to the flat character that is Rakgi's dad.
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