Tanjiro is a part the royal family. He has five siblings and he's the oldest. The second youngest is Nezuko. Then there are Hanako Takeo Shigeru and last is Rokuta.

You are going to marry Tanjiro. Not because you love him but because you have to continue the royal blood line and because both his and your parents decided it would be the best way. Now you were in your room waiting for him and his family to arrive. When it knocked outside the room and you told them to come inside one of your guards came in

Guard: Princess? The Kamado Family arrived.

You got ready and got downstairs in a minute. Tanjiro was stunned when he saw you.

Tanjiro: you must be the princess... I'm honored to meet you! My name is Tanjiro!

he told you that with a smile that looked like a never ending one. You could see that nothing could make him lose this smile.