Hagure Yuusha no Aesthetica

Synopsis

After a vicious battle, Akatsuki knocks Phil down. Thinking that neither Alayzard nor Earth are safe as long as she is present, Miu jumps into the river but is saved by Akatsuki. He talks her out of committing suicide and ends up kissing her before collapsing from a poisoned wound he received from Phil. Stripping them both naked Miu helps Akatsuki heal by sharing her body heat, though it turns out this was unnecessary as Akatsuki had been awake the entire time, much to Miu's embarrassment. However, Phil appears once more claiming he will no longer hold back against Akatsuki.

(Source: Wikipedia)