Game Market 1983 - Chapter 34

The ordinary 18-year-old Edo, during a nighttime walk, finds himself in a fantasy world where he gains a mysterious power that could shape his destiny.

After I defeated the Demon King, I was executed for false accusations by the heroines.When I came back to life, this was the first thing they said.“I know it’s shameless, but would you help us one more time? Without you, the world will be destroyed.”…Would you help them if you were in my shoes?

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

Akira Kuromiya is just an average high schooler who gets killed by a robber. He wakes up and is now a chicken!? Even worse he becomes the familiar of a girl who's apparently the heiress of a powerful clan.

That was for a short while though, as he was abandoned and woke up to find out he, now she, is trapped in a deadly magical forest with all sorts creatures trying to kill her.

The world she finds herself is one of magic and monsters like the manga she's been reading. Akira, now Hinotori is trying to live her life as a chicken in another world!