Pretty sure Ruti doesn't "want" to be a hero, just wants to hang out with her bro living the slow life. Yet, she's basically a programmed robot that doesn't need to sleep, has emotions that is constantly suppressed, doesn't have free will and must go fight against the Demon King. And on the off chance that her emotional program go on the fitz and she kills a comrade, she needs to heal them.
These flashback makes me feel he's a worst brother. He wanted to surround her with "reliable" companions. But the girl can basically slaughter everything on her own without any support. All she wanted was emotional support from her brother. He ditched her, plain and simple. And if I remember correctly, he wanted to fake his own death because he knew his sister couldn't take being ditched.