You need to get a Yokai weapon, these drop from enemies when you defeat them. When changing your equipment these will be purple. Use it lots until familiarity is 999.
Now when this weapon is equipped on the right hand side when you have equipped it you will see a meter which will fill up as you use it, when full it turns purple dealing more damage.
When this meter is full your weapon talks to you. Do this 5 times with a Yokai weapon and the trophy will unlock.