Well, from darks reaction it seems like he wanted to be kaydens disciple but something went wrong or kayden didn't approve of him.
But i don't understand what last panel refers to, what does he mean by making him move? Something we haven't heard about yet i guess?
Mangaka saw how popular his emotional moments are and started to squeeze every chapter dry for it. Literally every arc before this made me cry at important points, this one is pathetic.