What beep88 said. Send your large bags ahead to your hotel and just take a small bag with essentials as you explore Horyuji and Nara (both of which are excellent for history buffs).

Shipping one's bags is a common practice in Japan, so your hotel will be prepared to receive them. The shipping company (the main ones have counters at KIX) may or may not be able to have the bags arrive that same evening, but a small bag with essentials and a change of shirts and underwear will tide you over till the large bags do arrive.