Doh, I did not roll that :P. It's Mibu clan own lore so I assume I do not need roll for it :P. If he would roll he could have further idea that fourth guardian is related to earth and likely a serpent (borrow bit idea of world resting on scales of giant snake from Norse myth here) and that if you master all four you could learn the ultimate attack where fifth guardian (Ligthning; a kami of thunder/heaven) makes appearance along with four others.