Hero Hack: Reversing Heroes and Raising Harem - Chapter 15: Bones? Crushed

[You have entered the dungeon at Gwachun Station’s 1st Exit.] When former high school student Kang Woojin finds himself returned back to Earth after being forcibly summoned to a foreign planet for 20 years, he soon finds that Earth is not the same, normal place as he once remembered it to be.

Based on the popular Vocaloid series, by HoneyWorks, called “Kokuhoku Yokou Renshuu (Confession Rehearsal)“:

Natsuki, a third-year at Sakuragaoka High School, who holds unrequited feelings for her childhood friend, Yuu, who’s in the Film Club. However, instead of being honest about her feelings, she makes him be her confession “rehearsal” partner. Unable to say her true feelings, things start to get complicated when Miou and Akari, who are also in the Art Club, get involved! Will she ever be able to confess for real!?

On the will left behind by the 14 year old suicide victim K:

“Taku Sugawara is the devil. Nobody should believe his words.”

The fiancée has betrayed, but how could she know that the man she looked down upon was in fact a prodigy with healing and martial prowess!