spoilers
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You Huo used to be the head examiner of the system and at that time 001 was from the military and his mission was to infiltrate and destroy the system. So when 001 was taking the exam he would always break the rules and You Huo who was the examiner would always come to punish him (they also fell in love (▰˘◡˘▰) ). They both attempted to over throw the system together which resulted in the system wiping their memories, 001 then became an examiner and You Huo was kicked out of the system. Now they're reunited but You Huo who was an examiner became an examinee and 001 who was the examinee became an examiner which basically means they switched positions (just like the commenter said)
love how they switched positions....... lol u know what I mean if you've read far enough into the novel ;) (im trying not to say something specific cus that would be spoiling)