Is Yuuto him? Or did Yuuto just see her dream from his magic sword?
Hjiri was talking in her sleep so Yuuto must have heard her calling him "her Hero-sama" (the original line is "勇人さんは確かに わたしの勇者様でした!" if you're curious)
And I'm pretty sure the dream version is supposed to be
(no spoiler if you've read all previous chapters) Yuuto's father, seeing as he's the only one who's ever called him by his first name without any kind of honorific. Although keep in mind that the "dream hero" appeared in her dreams ever since she was young (cf. ch.1).
There's only 1 more chapter, so my guess is either both the hero and the devil decide to live normal lives and/or the series got axed and he didn't have enough time to write a real ending.
I've done some rather extensive research into Paper Braver and it seems to me that the mangaka decided to end the series on her own terms. You have to consider that this was her very first serialization, which also happened right after she graduated from high school, and that her next serialization was 4 years later, a.k.a. SukiMega.
I personally believe she just didn't know where to take the story and decided to conclude it by pretty much revealing every unknown variable (or at least hinting at them).