MC dies, meets god and decides to be reincarnated, he goes to the world of Solo Leveling along with the Naruto System.
MC will be reborn on the day Sung Jin Woo wakes up in the hospital after experiencing the double dungeon.
{Backstory of the Character}
The body of the character our MC will take over is the childhood best friend of Sung Jin Woo, He is an orphan however Sung Jin Woos family always treated him like family. Just like Sung Jin Woo, he was also a low ranked adventurer who goes into the dungeon along with Sung Jin Woo to help him with funds for his mother who is in the hospital with the 'Eternal Slumber' condition. He is also in love with Sung Jin Woos younger sister (Heh why not)
The Double Dungeon accident still occurs, however unlike the original where Sung Jin Woo was left alone to be killed by the statues, this time he his best friend also stays behind as the boy has nothing else to live for except his adoptive family (the Sungs).
{Backstory End}
The system is self explanatory so no need to talk about it.
You want to go along the original story in the Manhwa/Novel while injecting our MC into the story in the process.