Installation:

Copy and past the katana folder into:
Grand Theft Auto V\mods\update\x64\dlcpacks

Now open OpenIV and go to this location.
mods\update\update.rpf\common\data
Now paste this line dlcpacks:\katana inside dlclist.xml

Load the game. use Simple trainer by sjaak.
weapons - Spawn weapon by model name.
Type weapon_katana

Warning: Don't search-buy it from shop!! Also don't buy other weapons from shop as long as you use this addon weapon!!

Credits:

Model converted to grand theft auto V by: Sandra Linson
Model created by: BlackBradHz
https://el.gta5-hub.com/weapons/katana-sword-highpoly-4k
Database created by: yeahhmonkey
https://el.gta5-hub.com/tools/add-on-melee-weapon-base