100,000 yen should be sufficient, excluding your accommodations, transportations and theme park admissions, unless you're expecting to buy an expensive souvenir. I would carry a credit card for peace of mind.
Six coins are used including 1, 5, 10, 50, 100 and 500 yen values, alongside 4 bills/notes including 1,000, 2,000, 5,000 and 10,000 (although the 2,000 yen note is quite rare).
Luckily, it's a very safe country (one of our favorite things about Japan), and the biggest risk is probably losing or misplacing your cash. Regardless, of course, be smart and take reasonable precautions if carrying large sums of money.
You can eat well, using convenience-store food or cheap restaurants, for less than ¥4,000 per day. That would leave at least ¥6,000 for other expenses. So. unless you have expensive tastes, ¥20,000 per day is plenty for one person.
On ¥6 million, you can save plenty of money. The GDP per capita of Japan is about ¥4.5 million. 55% of Japanese women who are interested in getting married said on a survey that they wanted their future husband to make at least ¥6 million, while about 40-something percent said that ¥5 million was okay.