Roughly It takes place during the Tarten family's succession period where Christopher and Richard are one of the top candidates ( they r the side couple )they r not siblings but cousins to be precise
Ilay goes over as an official evaluator from the Reigrow family to help pick the next head. Meanwhile, Tae-ui gets sent to collect something from Christoph for Kyle, end up getting tangled in the whole Tarten family mess and their dynamic

Reading this so I can read Diaphonic Symphonia... wait for me Christopher