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After defeating a random A-rank boss Jin-Woo finds and odd key in where the magic core/crystal would normally be, but the key wasn't the odd part. The odd part was how the system gave him multiple warnings about said key, it almost seemed to be trying to persuade him to not use it. So he uses it, if the system seemed worried there must've been tons of strong monsters there...

It backfired the system malfunctioned and ended up erasing all his memories (except name), de-aging him, and making his powers very volatile. And to make matters worse he is dumped into a dimension filled with superheroes (The DC) that don't know how to handle the strange portals opening up all over the place.

So the system restarts and gives him Missions and Quests to complete in this world, with each quest he gains exp. points he can use to Level Up OR use them to 'buy' memories. (Note: This technically doesn't follow any given timeline from cannon DC nor cannon Solo Leveling.)