The Chois and Kangs have been each other's biggest enemies for centuries.
Prince Choi Beomgyu is the next heir of the Choi clan, and Prince Kang Taehyun is the next heir of the Kang clan. These two clans have never been friendly with each other at all.
The Choi family and Kang family had a meeting session in secret and decides to marry off their sons, Beomgyu and Taehyun for the sake of world peace. Marrying the two princes together might be the key for the Choi clan and Kang clan to finally get along together, even though the two princes are always at each other's throats for some reason.
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It's the first night after the royal wedding. Both princes are tired, but Taehyun is mostly irritated. He doesn't hate Beomgyu for simply being from the Choi lineage, no! Taehyun would never despise someone so much for such a stupid reason.
The real reason for the Kang prince's hatred towards him.. is because Beomgyu once accidentally murdered Taehyun's cat when they were 6. It was an accident, and Beomgyu was originally practicing using his bow to practice archery skills but instead, he had hit Taehyun's cat, Hobak. So Yeah — maybe Taehyun does hate Beomgyu for a 'silly' reason. (Not really silly because Hobak was Taehyun's only friend back then since he was isolated from other kids just because he's of royal status)
Now, they're sitting on opposite corners of the bed, looking away from each other like two siblings that got into a fight.
"So? What are we doing now? Act all lovey dovey like a normal married couple would?" Taehyun says sarcastically.