Duo was desperate against the enemy in front of them. She single handedly stopped all of their attacks. They used their boosting artifact which give them the power of a high sovereign but that didn't work either. Joseph was useless against such an opponent. His attacks wouldn't hurt her even they hit. So he ran away.
At the end boy looked fox girls eyes and they nod simultaneously. For the sake of killing that girl in front of them they decided to sacrifice a part of their conscious , their soul. With that way they could be low colosus for a short duration.
In that moment Jane gave up toying with them and appeared in front of the fox girl and kicked her with a great force. If there wasn't an artifact protecting her she would die. But she was alive thanks to it. As she hit a tree she was injured to the point she can't move. Thanks to her willpower she was still awake.
Boy jumped and swung his sword amd when Jane's and his weopons clashed he made the sacrifice. With that the attack Jane could stop easily became a dangerous one. Jane saw the increasing power. She understood that he made the exchange. For the sake of enlightenment he sacrificed a part of his soul to multiverse. He won't be the same person again.
Boy got stronger but he was still weaker than Jane. Jane evaded his attacks and countered.
Jane was a little bit stronger than boy with his spear.
While two clashed fox girl made what boy did. After she made the sacrifice she got up and made a great fire spell. Jane saw the spell and evaded it. With duo attacked they started to push Jane. And then something unexpected happened and duo understood their sacrifice was unnecessary.