This is from The Baby Prisoner of Winter Castle, in which a princess who is mistreated by her family is imprisoned/rescued by the stern and ostensibly unfeeling war leader of another country who kills her family but who, due to a legal loophole, decides to raise her until she reaches adulthood before killing her. The people who work for him then have to teach him how to take care of / pamper a child in the guise of rules for ethical treatment of prisoners.

Also her only friend is, literally, a pile of rocks? And when she gets to the enemy castle she tries to make friends with the stones the castle is made of?? But the castle stones are tsundere???

In terms of the character beats it's all very bog standard "child rearing romance fantasy", it's just those are all draped over a premise that makes me go cross-eyed