It all began when a womanizing hero, who had taken a liking to the beautiful childhood friend Milia, tried to kill the inconvenient protagonist, Jun, by throwing him off a cliff.

Deceived by the hero's lies, Jun believed his childhood friend Milia had betrayed him and lost the will to live. However, he regained his will to live through the persuasion of the Great Sage, Charmaine.

Having awakened after nearly being killed, Jun decided to aim for the top using his job, 'Efficiency Maniac' (Affisenlator).

'Efficiency Maniac' (Affisenlator) was a job where one earned points by defeating monsters consecutively.

Utilizing 'Efficiency Maniac' (Affisenlator), which allowed him to acquire skills with points, Jun steadily gained power.

It would be a lie to say Jun didn't harbor thoughts of revenge against the hero, but more than that, he resolved to train himself.

He desired power that would prevent him from ever being unjustly harmed again.

Aiming for the top, Jun became an adventurer in a dungeon city.

He rapidly raised his adventurer rank and made companions.

And those who witnessed Jun annihilating monsters during a stampede began to call him 'The Thunder Sage'.

This is the story of Jun's remarkable achievements, earning him the moniker 'The Thunder Sage'.

He hadn't been planning revenge against the hero, but the hero came seeking trouble.

The grown Jun effortlessly dealt with the hero, which led to the hero's downfall, eventually leading to...

What will become of Jun and his childhood friend Milia, separated by the hero's lies?

The title has been changed.

Old) Diary of a Thunder God Adventurer: [I Awakened After Almost Being Killed by the Hero]