Icksfolya, a world completely occupied by the Demon King.
This is the destination Isis told Duanmu Huai.
Not only that, she specifically gave a reminder.
"I think you must be wondering why we can only summon Heroes, rather than using our own Strength to eliminate the Demon King. Actually, the reason is simple. Just as we deities can give powers to Heroes from the Isekai world, granting them Strength, there are also deities that bless the Demon King. In other words, this is actually...…"
"To put it bluntly, it's a Proxy war."
Duanmu Huai was not unfamiliar with this. Clearly, the Unified Divine Realm is on the side of Humans, while the deities on the other side are on the side of Demons. The two sides may have had direct confrontations in the past, or maybe not. But regardless, the situation has developed to this point, and it's now essentially a contest between their proxies.
