The two battles are happening simultaneously, but at different intensities. One side has only the life of Mier on the line, while the other side has the adventurers staking their lives on the line. One vs. Many. Yet, the stakes are still high enough that it is considered something very hard to deal with. And the thing that is causing this issue is none other than the same monster that the two sides are fighting, the serpent Leviathan.
Right now, Elaina is still pouring the water coming out from the blessed watering can to the leaf-covered arm of Mier that is somehow showing signs of fighting back by forcibly controlling Mier herself. Mier shows signs of fighting back, but since Mier is still a child, against a monster caliber of the Leviathan, Mier is no more than an ant that is struggling against a giant enemy.
