Tales of Berseria's theme revolves around the relationship between emotion and reason, and how this relationship differs for each person. Members of Velvet's party boast varying degrees of emotional impulses and reasonable decision-making skills, oftentimes leaning closer toward one over the other. Velvet is strictly emotional; Eleanor strives to emulate reason by stamping out all emotion; and Laphicet serves as the natural middle ground by absorbing the values of those around him.
While Eizen is a romanticized portrayal of a free-spirited pirate, he also illustrates the middle ground. But unlike Laphicet, his emotion and reason coexist in an inversely proportional relationship.
Eizen is selfish: He reminds Velvet time and again that he's there for self-serving reasons, and he tries to abandon her more than once whenever she would become a liability. He passes his days in piracy instead of returning home to his sister, who would rather have him back and suffer the consequences of his curse. A sidequest involving a series of anonymous letters, voicing how cruel his distant treatment of Edna is, highlights Eizen at his most selfish, and he acknowledges that he has wronged his sister by putting his wants before hers.
On the flip side, Eizen is self-sacrificing, insofar that one might consider him noble. In Berseria, emotion represents selfishness, while reason embodies selflessness at its best and worst. When Eizen dips into the latter, he puts aside all of his personal desires, even if to his detriment.
Eizen is a malak—a spiritual being attuned to the element of earth. Every malak is capable of generating a blessing that grants a boon to those within their domain. Eizen's blessing, which promotes growth through grueling trials, is largely regarded as a curse for the fact that it causes harm and even death.
When he learns that devouring the heart of a white-horned dragon can lift his blessing, Eizen seems to consider this. In the end, he chooses to let the creature die with dignity, because dragons are born from malakhim who have absorbed an insurmountable amount of malevolence—impurities born from the negative emotions of humans. Eizen states that transforming into a dragon is the cross all malakhim must bear, and so he declines to do anything that would spit on the malak who has turned; in doing so, he loses his chance to cure his curse and sacrifices any chance he'd had of sharing a peaceful life with Edna.
The extremes to which he swings brings a certain level of complexity to Eizen's morality and makes him stand out against the rest of the party. As the eldest member of Velvet's entourage, Eizen boasts the grace of having already undergone his cognitive development, and his certainty in his current way of life becomes the anchor that grounds the lost Laphicet, who has just started to develop his individuality.