@BlankDevil Brother got isekai'd or something, joined a powerful group, wars started to break out due to the promise of a wish at the top or something, people constantly betray and kill eachother, brother gets the Elixer to heal the already passed away Mom too late. MC swears revenge on the ones who killed and betrayed his brother after starting to inherit all of his brother's abilities.
That's just what I interpreted. Basically he left a long journal, and after the MC read/watched it all, his brother's abilities and items are presumably being transferred to MC.