Alright so first, corruption? Is this a forest thing, a tower thing, or not a thing and just how they get rid of problems? We may want to talk to this corrupted individual, see if they did something to become this way.
Ok so the boar mask gets Cherchiel back to full strength... If you can keep Yulias pants on. Cherchiel, use the mask when you need to protect Yulia and make sure to channel those thoughts. In this case, Lumberer wants your woman, don't let it touch her.
And now Lumberer... So we still don't have a spear you Cherchiel, but would Boarchiel want to use a spear? We're rested and able to fight, the question is does Boarchiel think her returned strength plus energize is enough to wrestle Lumberer? If that answer is no, then retreat until we get the spear.
If yes, battle plan time! Enegize Cherchiel and have her engage Lumberer. Transform into Boarchiel as you head over and remember to focus on protecting your woman. Once engaged, Yulia you flank Lumberer with energize then try and land stabs on its back. Keep your mana for healing unless it seems that Boarchiel can safely match the Lumberer's strength. If Boarchiel had a weapon we could have had Yulia go full healing mode, but until then your still the best damage dealer.
In terrible circumstances... If Boarchiel turns out to overestimate her strength and gets thrown like a doll... Yulia you have the Halo. Buy time for Cherchiel to retreat with Muma by engaging with energize and doing your best keep away. Once safe make a retreat yourself unless it turns out he's slow, then maybe you can poke him to death.