Honestly, according to spoilers, it’s cause the sister freaks out any time her sister is mentioned because of the guilt, so bright literally made everybody around her not talk about her(which is also messed up.) Bright is selfish and the sister is ignorant in bliss because she can’t even face her sister giving up her life for her. It’s a horrible thing, since the sister was actually the only one that didn’t wish for mc to replace her, but she should at least face the fact that mc made that sacrifice and stop the backlash against her. She’s selfish in her own right, but the main offender is definitely bright and her adoptive parents
Real talk like why the hell did the sister even let the rumours go out of control about her sister in the other world. Like seriously you care for her but still won't clarify. Bye.
P.s both the sister and her husband are shit parents. Like I'm sorry your feeding your husbands inferiority complex by putting your own son down and telling him he shouldn't use his magic, just so that your husbands feelings don't get hurt. That's horrible. If he feels great using magic and is a prodigy in it you should be like well done not like don't use it your father doesn't like it. Like he literally uses it to protect your empire yet everyone is bare ungrateful.
Okay bye now.