Astrid Zexis is an alchemist and mentor to Rorolina Frixell. She took Rorona in as her pupil after curing Rorona's parents of their ailments. Despite her intelligence, Astrid is highly lazy and prefers to sleep in most days. She was the owner of the Arland alchemist workshop until she heard news of the workshop's impending closure, where she transferred ownership of the workshop over to Rorona.
Astrid is a keen observer and steps in whenever she notices Rorona going into a particular conversation or situation. She tends to get a quick feel of what Rorona's friends are and acts accordingly to protect her.
When Cordelia asked Astrid why she took Rorona in as her pupil, she responded that Rorona was 60% cute and 40% dumb. Astrid explains her "dumb" answer by stating that Rorona has a special case of dumb where she'll go straight into a task and will persist at it until the task is accomplished.
Astrid created Hom, a homunculus, after inquiring Rorona if she'd be happier if she had a younger sibling around. She purposely produced Hom to be 4 foot 8 inches, an inch and a quarter higher than Cory, just to make fun of Cory's short stature.
She was formerly in a relationship with Sterkenburg Cranach, but they fell out due to the severe differences in their personalities, with Astrid being the intelligent yet lazy one against Sterk's diligent, hard-working attitude. Astrid confronts Sterk as she noticed that he's been around Rorona a lot whenever she ventures outside of Arland to gather ingredients to synthesize particular items.
In the end of Atelier Rorona, after Rorona successfully passes all of the kingdom assignments, Astrid told her the true intentions why the workshop was in danger in the first place. Astrid spoke on how her alchemist master was similar to Rorona, a very nice person, but clumsy and not skilled in alchemy. The Arland townsfolk didn't care for her master as well and eventually was exiled from Arland. Her master passed away soon after her exile. From then on, Astrid held contempt toward the Arland Kingdom and townsfolk, refusing to perform any jobs which led the workshop to its state of closure. Then she tells Rorona that she'll be leaving Arland and plans to run an alchemist workshop at her master's hometown, and leaves Rorona alone to run the workshop in Arland all to herself.