Just use the active skill of whoever gets the (!) over Wanpa. Itsuki's job is to heal everyone and keep buffs up, as well as to target the axemen whenever he can. Yashiro and Elly can target the axemen too if the turn order doesn't line up well for them.
You can do this fight pretty early if you have ice blocking gear for Elly, Itsuki and Yashiro.
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