After discussing with Robert, Nathan decided to delay making a decision and instead spoke with his fellow party members first.
"Robert informed me of the possibility of stronger monsters existing in this pocket dimension, and how it could affect the battle between the various parties within it. Consequently, he proposed an alliance between the top 10 parties on the leaderboard, in order to unite our strength and increase our chances of success, thus avoiding defeat due to a shortage of manpower." he explained.
However, as usual, they left the decision totally up to Nathan, not showing the slightest concern. This occasionally annoyed him a bit, as he wanted to hear their opinion. "You're really too passive, guys," he said.