Zhen Ji - 5th Weapon | Dynasty Warriors 3: Xtreme Legends (4K, 60fps)

This one is probably one of the easiest 5th weapons to get, because as soon as Wu Chao burns down (Which you have to do) your forces will steamroll Yuan Shao. There is also a trick to this one, making it easier, but depending on the version of the game it might or might not work.

Difficulty: Very Hard
Stage: Battle of Guan Du (Original) - Wei Forces
Requirements: Find and enter Wu Chao on the 4th try (You have to enter 3 incorrect ones first)
Location: To the east of Guan Du castle, north west of the giant rock

Tips: If you go right next to each of the compounds you will see if it's the real Wu Chao because it will have storage Silos in it (Cylindrical towers basically), however, I like to defeat and open all the gates to the compounds. Save and then enter each one to find out if it is Wu Chao, When you've found out reload the save and make sure it's the last one you enter.
The looking in stat doesn't work on emulation all the time, it depends on your settings as well as depends on where you are looking in the compound from.