Ankoku Kishi no Monogatari
M.C was summoned by the This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.
Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.
“Please save us, Savior Dono!”
Kuroki nodded, deciding to save the demon king due to an unexpected turn of events!
Honestly this LN is very polarizing due to the M.C being bit soft and infuriating because of the hero that you will want to punch in the face hard because of how self righteous and careless he is, but this is really a fun novel though.
And that armor is really cool, reminds me of Berserker from fate/zero.
@Zeronos You should make a more complete and structured post, add pictures, the length of the series, the name of the publisher, the author, and the illustrator.
LNDB is down now but you could link to the MAL, Amazon, or Bookwalker page of the series. Also, there is a problem with the beginning of the synopsis.
You should look at other licensing posts, they tend to follow a pattern.
@Raitoiro oh no, it's my first time to suggest, but thanks for the help.