If you provide a short summary of chapter 99 (or key scenes you want analyzed), I’ll incorporate that; otherwise I’ll assume only commonly known series context and analyze more generally.
Chapter 99 is being treated as a pseudo-anniversary chapter. In manga culture, chapters 99, 100, and 101 often form a trilogy of big reveals or climactic moments. Fans are speculating that Chapter 99 will serve as the launching pad for a major confession or a dramatic misunderstanding that will set the stage for the 100th chapter celebration.
Many harem manga introduce a male rival late in the game. Leakers hint that Chapter 99’s final page will introduce a childhood friend of the sisters—a handsome, talented boy who looks down on Toru. This would raise the tension going into Chapter 100.