Monster Hunter Story (The Mythic hunt)

When they were celebrating a party for Arithia,Lolita and Hiyama suddenly Arithia meet with a unknown person which tell her ' it's not a time to be happy " Arithia was so weird cause he saying a things like that so Arithia ask him ' Why? We already kill Aprho and bring the peace" Then the man say to Arithia ' Maybe you're already kill that monster. but there has something you didnt know about this world"