Thanks to this part of the Guide Monster Hunter Stories 2, you will be able to discover all the elements relating to the main quest "The end is near". You will find here the complete progress of the mission as well as information on the Bosses encountered.
After activating the quest, head towards the Guardian Ratha Forest and cross the entire area towards the lair to the north (pictures1-2). At the end of the cutscene that will be triggered there, enter the Forbidden Lands to face the Destroyer Ratha (picture3).
To win this very easy fight, counter the strength of the monster with speed while healing the group with powder of life after each of its area attacks (picture4).