But how it could be abused? I think old manuals you can get only at start and won't see ever again. Yeah, you can exchange old manuals for normal ones and normal ones (you get 2 old manuals) for 1 HE manual. But you need 40+ for that.
You really dont see abuse at all? I fully admit to abusing it myself. Have an extra slot on your account, Make Kunai Ninja, get Kunai ninja to level 40 in 10 minutes. Get infinite supply of Battle Manuals.
Besides converting them into an HE manual for 2 and vending them, which people DID DO. You can get infinite manuals to use on your other characters without ever touching the Kafra shop. This was something I only shared with a few of my guildmates as I was hoping the GMs didn't notice it.
They finally took it out though so I couldn't have inifnite battle Manuals anymore.