@icekatze umm are we reading the same manhwa? there is absolutely nothing cruel about this ML. he explicitly asks ebony what she wants out of her life right now. if she wants to go to study, he will send her to a university. if she wants to hide, she can remain forever in the castle. if she wants to start a family, he will find her a good man. basically whatever she wants, he will help her get it. and if she wants revenge (on those who abused her, which is quite general, probably the Kalcass society), he will help her. he already has a plan in place that is like killing two birds with one stone. however, since Dante is an extremely powerful man, if he were to actively pursue the mansion himself, the noble society will not leave him be.
that's why he asks for ebony's help. and she says she will be his chess piece in carrying this out because she will be the masked individual who will be attending these meetings and interacting with the noble society. he wants to overturn the misogynistic and backwards value of Kalcass and to do this, he must gain hold of the academy that is associated with the meister mansion. unfortunately, general meister is dead and as customs dictate, the men of the family are the ones who typically inherit the mansion. originally, dante was going to have ebony go in and participate in the meister games (probably like gambling) to win the mansion. however, ebony suggested that a better blow to those noblemen's pride would be if a WOMAN inherited the mansion instead.
so the new plan, is to help the meister's widow gain custody of the mansion, and they get the academy in return.
you also seem to be misunderstanding what the meister game is. it appears to be an auction/gamble for the mansion. has nothing to do with a murder conspiracy. the murder conspiracy you seemed to be confused about might be the one in which ebony killed the previous sedell head. but what happened should be pretty obvious. she most likely killed her fiance out of self defence but because of how backwards and misogynist Kalcass is, they completely overlook that detail and branded her as a murderer without investigating her motivations behind it.
the point of them winning the meister game is so that a woman may inherit the mansion and so that dante's faction may gain hold of the academy. controlling an educational instituion is akin to controlling the country's military because that is where you train and teach your values. for the men who looked down so harshly on women, seeing a woman in possession of the meister mansion will be a huge blow to their pride and values. if ebony is able to successfully aid the meister widow in gaining the mansion, it will be revolutionary