Responses
In the novel it was not written that they end up together, im pretty sure Eckhart (CP) know rere is his half sister, maybe he does feel affection for her but not romantic love, but this is for the Novel part, i dont know if the artist will change the ending with some surprise (eckhart is not emperors son or so)

The only unanswered question of mine is - who tf is CP's mom & if CP's dad really is emperor i hope nothing romantic develops between rere & CP since that'd be incest cause it's implied that emperor r@ped ML's sister therefore if CP is emperor's son CP & Rere are half siblings