Complex sentence: The SSS fight against Kanade Tachibana, also referred to as Angel, the student council president of the afterlife school whose responsibilities require her to suppress the team's disruptive activities.
Split into simpler sentences: The SSS fight against Kanade Tachibana, also referred to as Angel, the student council president of the afterlife school. This places her at odds with the SSS as her responsibilities require her to suppress the team's disruptive activities.