I will arrive at Haneda Airport at 19:00PM and depart from Narita Airport at 17:25PM the day after. Hence, the time spent staying in Japan will probably be around 20 hours, including one overnight stay.
I am preparing the required documents to apply for a transit visa as my itinerary requires me to change airport. According to the Japanese Embassy website, there is one requirement:
If stay in Japan exceeds one night: Proof of sufficient funds (e.g. most recent U.S. bank statement, travelers' checks or letter of guarantee from friend/relative in Japan).
I don't have my own bank-account or a credit card yet as I am currently a student and my stay in Japan is less than one day, how should I present the "proof of sufficient funds"? It is my plan to bring about 20,000 Yen in cash to cover any cost that may arise during my transits.
Edit: I am applying for the transit visa in my home country and the "proof of sufficient funds" is one of the mandatory documents. What I fear is that my visa application might get rejected, and if it happens, it will happen in my home country, not in Japan. Hence, the problem is not with the Immigration Officials in Japan, but with the Japanese Embassy in my home country. If I could get hold of the transit visa, I don't think there will be any reason for Immigration to deny my entry into Japan.