I'm going to spoil the plot and ending of Ys: The Oath in Felghana in this page. Chester Stoddart was a descendant of Genos, who vanquished the evil Galbalan many generations ago. Galbalan was split into four pieces and trapped in statues, which were hidden throughout the land of Felghana. One day, his home of Genos Island was massacred by a mad man seeking to release Galbalan. Still children at the time, Chester and his sister, Elena, were the only survivors.

Years passed and Chester became a knight, working for Lord McGuire, the man he believed to have ordered the massacre, with revenge as his goal. When Elena found out, she opposed the idea, as Chester intended to use the power of Galbalan for vengeance. That would inevitably involve innocents, though he didn't intend to go as far as freeing the monster. Later, Chester realized he was being used and regretted his actions. In the end, he sacrificed himself to permanently defeat Galbalan.

Chester was from Genos Island and Wystern is kind of an island, albeit an artificial one, being a tower in the sea. Ureksa and Chester both have positions that carry certain duties: Craftlord of Jade and descendant of Genos, tasked with making sure Galbalan didn't escape. They pretended to work with Lubert and McGuire respectively, both of which turned out to be more so pawns than masterminds. They were willing to attack their friends and allies for the sake of revenge, with Ureksa imprisoning Tyram and Chester injuring his childhood friend Dogi. They suffered because of the influence, direct or indirect, of a powerful creature that was somehow trapped and tried to use that power for vengeance later. They both fight the main character, Adol and Cleru or Pratty respectively, several times during the game.

Chester and Ureksa have look-alike sisters whom they care about very much, though Elena is younger than Chester and Rumari older than Ureksa. Rumari and Elena tried to stop their respective brothers from pursuing revenge. We know Chester and Elena lost their parents, as for Rumari and Ureksa, it's pure speculation, but maybe they did too, since they were never mentioned. Also, the way Ureksa acts towards Rumari hints that she might have had a role in raising him beyond that of a sister.

Ureksa tried to commit suicide when he was consumed by guilt. Chester sacrificed himself to permanently defeat Galbalan. They were both driven by the wish to protect their sisters while carrying their guilt. Albeit Ureksa's death, if he had not been saved, would have been in vain, Chester's sacrifice did finally destroy Galbalan.

In Ureksa's case, the other Craftlords knew what was going on, but didn't confront him. In Chester's case, other than the man who saved him as a child, who chose to remain silent, no one knew of his tragedy. Elena's memories were suppressed and she didn't recover them until Chester was already in the middle of his plan. Even so, they both had people who they could have talked to, but for various reasons ended up dealing with things on their own. To summarize, their respective stories have a lot of similarities, an evil creature that's trapped, thirst for vengeance, a sister with a wish to peacefully move on. They go through similar processes of bottling up their frustration, trying to carry their problems on their own, doing some rash things and regretting their actions.