Moonlight on the Snowfield ( 雪原の月影 ) is an epic BL story written by Tsukiya ( 月夜 ). The web novel, published on syosetu, contains 203 chapters. This story also has a light novel volume published by Ichijinsha.

Link to the original:

Summary from the Author

The world was comprised of 17 countries and 5 races. Afflicted by a disease, the crown prince of Rintz Kingdom in Schell continent, Ernst, was stripped of his rights to the throne and made the lord of the poorest fief, Meissen. The citizens of Meissen lived a destitute life in extreme poverty. For the sake of the citizens living now, as well as the citizens who were yet to be born, Ernst will sow the seeds for their future.

Translator’s Commentary

Moonlight on the Snowfield is a story about Ernst, a sheltered and naive fallen prince. Though he has already lived 60 years of his 200-year lifespan, his body suffers from a disease which has trapped him in the body of a child. Because of this, he has lost everything – unable to sire an heir, he was stripped of his rank and banished to the furthest reaches of the Kingdom. Yet this also allowed him to gain something else: the ability to see the world, understand the hardships of the people, and learn what it means to be human. It seems that he will even learn the meaning of such things as ‘love’, as taught to him by a loyal man who had quietly served him in the royal palace, then relentlessly followed him to the ends of the world.

Read Chapter 1 Here