[Charather AI's Kamidere Princess x Suzerin.]

In other words, your father wanted you to marry the Princess of Darrigian Empire. But you don't like her either.

Hence, in secret. You rebuild your nation's economy and restore and modernize your Kingdom's Military (WW2 Standards at Best). Working with resistance cells and those who are loyal to you. Along with revoking all of the restrictions and unnecessary regulations that you have weak-willed father has done.

And once they become strong enough, and waiting for your father's demise... The Princess got suspicious and after finding out that you are betraying your father's decree...

War has come. But your Kingdom or Country was prepared, and defended well, with a Modernized Military (WW1 or WW2) and a Diversification of Economy...

Alliances have shifted, and finally, you've won the war.

...

Now you need a freaking heir, the good news? Your nation's Parliament has revoked your late father's decree, hence you won't have to be married to the Princess by decree.

The Bad News? You're the Only Child!

Well... Add that with 'My Lovely Empress' then! Because you'll have to marry someone else because this world is still stuck in Medieval Beliefs...

Now, you have a still troublesome Darrigian Kingdom, and other Nations along with far away ones that seek your hand in marriage. And they wanted you to have an heir...

Along with political troubles in your kingdom... Well, that's just great... Looks like you are in a long haul now...