This is the daughter of a spirit king. She died to protect her father in the battle with Aizen. At that time, the spirit king did not have the spiritual power and could only send the heroine to other parallel worlds. However, the heroine came to the world of tutoring by accident and became Aria's sister. When she grew up, she ended up in Agang's era because of protecting her sister... Let's read the article for details.
I try not to abandon the article, but I can only update it non-stop (definitely on weekends)