In the True Cross College, there is a course that almost no one chooses - "Spiritual Biology and Oriental Anomaly Research".
Ji Ji Ling, the teacher, has two biggest worries on a daily basis: students would rather skip classes than study those terribly complicated spiritual creatures; and Mephistopheles, the chairman of the college, has nothing to do but trouble him every day.
Until one day, Mephistopheles secretly replaced the open class courseware that Ling had prepared for a long time.
It turned out to be just an ordinary revenge.
Until Okumura Rin walked into his class.
A boy with blue flames.
A child with a special connection to Satan, the Lord of Demons.
And a teacher who can also control green flames, but has never explained the source of his power.
When Ling showed Qing Yan in front of everyone for the first time, something started to go wrong.
Why did the Demon Royal Family show unusual interest in him?
Why does Mephisto know the answer but never explain it?
Why can his green flame choose what to burn and what to leave behind?
And the existence recorded as the "Contract Demon" by the Knights of the Cross——
Did it ever really exist?
This is a story about green flames, demons, choices, and a "king" forgotten by the world.
Purpose: Being able to choose is more important than anything else