The mother had an illness which disappeared because of MC but she thought it was due to her sister. She later felt sorry for what she did and died due to illness
The sister was locked up for being a fake. Initially she thought why this was happening to her but slowly started to realise she was not special. The princess rescued her and she slowly changed.
But, the father kept cursing the MC for all their misfortunes, he was angry that she was not grateful of 'being raised'. The priests thought 'this guy has no remorse'. The wife got ill - mc's fault for not being grateful. He was locked up for mistreating mc - mc's fault for not being grateful. He became a slave - mc's fault for not being grateful. When he heard that mc is the real miko, he was worried about MC's sister that she might mistreat her. Even till his death he had no remorse and hated the MC, because it was her fault for not being grateful. When mc was 5 the mother didn't hate her. But the mc was bullied by the kids and when the parents arrived the father got angry at the mc because it was her fault to make them feel inconvenient. So, the mother started hating her since she loved the father.
I don't get the father. Why go to unnatural lengths to hate a gifted child ?

She makes up with her sister and perhaps even parents. A commenter says her dad gets eaten by a wolf but i kinda find that hard to believe since the only Wolf would be Gauis. She still protects those two kingdoms and temple in the end. Which sucks.

The excitement dies down after the King dies. When he played a part as well but in the end didn't see anything through. Simply put, things are too convenient. Gauis dad dies and Ramo as well which is pretty much the MC fault and could had easily been prevented but i guess it needed the dramatic effect. A lot of things become insignificant. With the Temple and Kingdoms, all become in peace. I wish they where tare down. I wouldn't mind if Miga Kingdom and Human Kingdom combine together for peace.
The romance with Gauis is ok, I don't really like it or dislike it, but it's better then other romances i guess. The best Romance would probably be the 7th Prince and 5Th Princess, now that Romance was good!

Like i said don't expect too much, it's mostly about the MC growing as a character. It could be cooler but it doesn't really take that route we're use to seeing. We can't call this a "kingdom building" it's just gathering people.

Basically the MC was different then the others in the village, and and they felt the sister was special due to her appearance, as a result they never tried to understand or bond with the MC.