This latest gem is what Twitter user @xxSeri hilariously calls "Ishikawa stock". The gist of it is that Jin can only carry so many arrows at any one time, and if you're using your bow a lot in battle, you can quite quickly run out of ammo. So, in order to carry more arrows, xxSeri simply fires a few of them into Ishikawa's mostly bald head.
There's no friendly fire so Ishikawa isn't damaged by the arrows, and when Jin's supply is running low, he can just walk over to to his sensei and restock, automatically plucking them from the old man's noggin. The only catch is that you need to have a specific Charm equipped that allows Jin to recover used arrows from targets.
So dumb, but so effective.