I can really see this game story developing like diedritch? Train the prince and dregade him more until he opens himself with him, and tells what is making him not wanting to love anyone. Something like his mother had loved his father completely but his father didn't return his mother love and she went insane, start to seek pleasure with other, try to cause jelousy in her husband, create scandals, but nothing worked and the king found another wife? His brother's mother. When this happened the prince mother mad and exausted tried to assassinate the other wife, and was executed and thats why the prince was a virgen and tried to avoid relationships. In this point we can have like two finales, one that ur actions in game made diedeitch discard the prince after he had fun and trained him staying that he was boring and command him to serve as a monster nusery/hatcher and another that diedritch really falls a bit for him and have him remaing by his side and eventually leaves his seed in him. After some years the prince father see his kingdom fall apart because his sucessor was easily influenced, and goes seek his abandoned son out to help him or the stone that the prince wanted. In the first path the ex-king and his soldier goes through the florest killing beast until they found the prince that is now just a recipient for the monster seeds, without will or soul and he didn't even talk anymore, and they decide to kill him for not let the monster population increase, diedritch appaers too late to kill the intruders and kay was shot and is dying,. In the second path when the ex king try to enter in the woods and start killing monster, diedric appaers and shows them the prince, everyone is shocked to see that the fierce prince is now submissive and a father, and the prince just look at them and says to didritch "i don't know them, my only family is master" and turns arround and walk away while diedritch kill everyone.
P.s. nine could be somekind of incubus and help in some sex scenes or punishiments too