
The main character is reincarnated as Ash, the character of the game he was playing. However, Ash was a so-called "helper character" who helped the main character in the early stages of the game and was later killed by the enemy. The only thing he can use to live as Ash is the knowledge of the game. In order to change the fate of himself and his favorite character, the villainess Mercy, he sets out to conquer this world. (Source: Brave Bunko, translated)
Otasuke Chara ni Tensei Shita no de, Game Chishiki de Musou Suru is a Japanese novel of 219,743 characters, with 9,656 unique words and 1,930 different kanji. Its difficulty rating on Jiten is hard, 3.3 out of 5. The full vocabulary list ranks all 9,656 words by how often they appear, and you can study them on Jiten or download them as an Anki deck.
Here are some of the words that appear most often in this media, as well as a sample of its rarer vocabulary.