Surprisingly effective
Himeko swung her great sword into the boss to see the kind of defence it had and if it was even safe to touch. The boss did not move at all, taking the full force of Himeko's attack. Turns out however, that it didn't need to move at all as it came out completely unharmed.
Instead, Himeko's flames caused a reaction with the demonic magma. As it came in contact with Himeko's flames, the boss's chest started bubbling like it was about to explode at any second. Not taking any chances she pulled away her great sword while creating a magma shield in front of her.
And not a moment too soon. Just as she expected the boss exploded like a volcano, releasing purple magma rapidly from its chest. The heat was so great that the floor around the boss turned into a magma pool, making it impossible to approach without protection.
Luna quickly cast her support shield on Himeko. This was demonic essence they were dealing with, so she wanted to make sure Himeko was fully protected.