In the season 6 onwards routes, Klaus is more like an older-brother figure to the protagonist. He's so overprotective of her that even Zeus gets jealous of his "constant interfering" and wonders if Klaus is interested in her as more than just a friend. Although one of Klaus hobbies is teasing and mocking the protagonist, he appreciates her so much, and recommends her as a Prefect Candidate. Klaus II allows her to handle difficult or dangerous situations because he trusts she can come out safely.

Klaus’ relationship with his older brother (Alfonse Goldstein) is a complicated one. For work, he will tolerate being in the same room as Alfonse. However, Klaus often rebrates Alfonse (not in front of the other characters, only in front of the protagonist) and pretty much makes it clear he hates Alfonse. Klaus resents Alfonse because Alfonse was supposed to be the head of the Goldstein family. However, he chose his research over his family, and just left one day, leaving Klaus to be the Goldstein heir. At a younger age, this gave Klaus a lot of pressure.

His personality is still pretty much the same as the one in the prior seasons. Klaus is characterized by single-minded intensity, as well as a harsh, unforgiving, and frequently caustic demeanor. Beneath his exterior harshness, however, he is well-meaning and kindhearted. Klaus is now currently working as an investigator for the Ministry of Wizardry and Magic.

Voice: Mid-deep to deep, mature, ole enough sounding for someone who is 25+ years of age, open to interpretation.