secret characters will have a branch off the main routes, while it might start with an affair of some kind, as those characters decide to pursue/monopolize you. eventually leading to sometimes death(male lead death)/second kidnapping/or some other scenario. Into a new route ;).
As for the upcoming characters:
Cyrus is a very detached character(hes super handsome too), he's very cold, evil, insect-like in a way, Id like to say he's a parasite? hes mentioned a bit in the story, signifying the fear the other characters have of him. It makes him, one of the big antagonists, he relies on hypnosis, wanting to use you for war and to break rules.
as for Harlan...
Harlan, broke his rule too much, and is essentially on the verge of going insane, he's developed a more animalistic sense of mind, desperate for a lifelong mate. only issue is male calicos cannot breed, so having kids is not going to happen, all the fun and no kids, he's sterile(poor guy). Harlan's a real mental case/completely obsessed, I did half complete his route to some extent(his kidnapping scene is already done and his art is partially finished).
secret character:
if you encountered the window scene at the end, then you found him!! ;)