As he was shown this chapter as one of the 2 people looking for her and someone spoiled that at ch.09 gramps will tell her all this and give her a small PTSD moment, Rhonya's brother is looking for her. The reason is unknown but it can be between 2 things
1. His own personal punishment for embarrassing the Gavisera name. The Gavisera family actually have a bad rep for being talented but "ambitious", Rhonya's bro is classmates with her mentor, Gretia/Grey/Gray (introduced at Vol.02, a purple haired man, sporting a ponytail, and is mostly shown emotionless/apathetic but actually just has trouble expressing/understanding emotion. It is implied Grey is romantically attracted to her and Orphedoto is the captain of this ship) and both are the top of their class, but bro was forever the #2 and Grey was the Valedictorian and hence is now the Royal Magician of the Kingdom. Dunno what is bro's current job. Back to the ambitious part, this actually helps Misano back at Rhonya's departure seeing as back in Rhonya's academy days, the only people acquainted with her are Schneider, Hansel, Lexi, and 3 random noble lady supporters/orbiters (the same 3 noblewomen who testified against her. Random add-on, MISANO F*CKING DRUGGED those 3 people just so she could have someone testify against Rhonya. Will talk more about that later), the rest of the students don't particularly like her but are acquainted with her for the sake of Schneider who will be king (plus it didn't help with Rhonya being a natural introvert and was busy doing her responsibilities both as a contractor with the spirits as well as doing her responsibilities as the future queen by being a diplomat, funny thing is 2 kingdoms want her to stay with them right after Schneider annulled the engagement)
2. At this point in time, it is implied this is where Schneider either starts looking for her because he's being nagged by the important side characters and calling him an idiot/moron for the nth time (side characters being Hansel, Lexi, and his uncle the King) or realizes his mistake and ends things with Misano. If it is the latter, despite publicly annuling the engagement, the king naturally prefers Rhonya because you know, he actually knows her, is competent, and SHE SAVED THE WORLD and only a few people know about it. So ofc bro might be trying to take advantage of the situation and force her back (this is my assumption)
Why Rhonya is scared of him: mental abuse and a little bit of physical abuse. Mental for constantly belittling her efforts (and I guess pissy that she's the top of her class while he wasn't with Grey around) and the fact that if she DOES get achievements, her family just gives her even more responsibilities and the process circles back to belittling. Physical: Blaming a sick person (when Rhonya has a cold) for getting sick.
Vol.03 mentions his tone is very authorative (basically, our girl can't handle the strict military style tone). This is the same reason she rejects the elven prince who proposes to her later (but prince is a good guy and one of the few men Schneider was wary back when he and Rhonya were together)