@marssel important to the plot? Remove the arc completely, the kids graduate, then MOVE ON. Not only is absolutely unnecessary, Toki should be in jail for all she did. If this were a power fantasy story I'd understand the journey of redemption but this is a very very grounded story, those things doesn't happen (and shouldn't either)
sorry but that's about Japan, they have veery different culture related to their respect to society layers. I think author wanted to show how narrow minded they can be due to that trait so as the caracter's growth