In a miner town, the Radiant, where most of the finest metal and ores are unearthed.
The King calls for people with age above 20 for the His Quest.
Men and Women will be put through an expedition in far far land calls "The Bad Land".
The Quest is simple, kill a dragoon. It sounds more like an execution for everyone who enlisted in the quest.
However, the real reason He wants his people to go through is purely experiment purpose.

To keep it simple;
Get a bunch of people from every town in the kingdom, send them with experimental weapon to kill the beast, record the result, repeat until the beast is dead.

Mary is one of many that were enlisted to a platoon. This is foreseen as her parents were one of the lucky few who made it back and have a family.
They all know when the time comes, there is no denying on the King's request as He has given a lot to people. This is the only way to repay their loyalty.
Most of metal weaponry are made in the Radiant, but the people of the Radiant does not know how to proper use them, to put it simply, they are meant to use their raw strength instead of their skills.
With many brutes in high quality gears, it is very likely most of them will get a higher chance of surviving a dragoon encounter.