Sarah Outen, from Rutland, is trying to circle the globe by cycling, kayaking and rowing.
The row across the North Pacific to Canada is expected to take six months.
The 27-year-old's new trip had been delayed again by several weeks due to poor weather but she left Choshi Marina at 15:33 local time.
"Butterflies have arrived and my head has now clicked into very focused mode," she said.
"It has been a massive mountain to get back to this point after last year's rescue," she said before leaving in her new boat Happy Socks.
The storm sank her boat Gulliver in June 2012.
She is hoping to become the first person to row single-handed from Japan to Canada.
"It's not a given I will even make it across successfully to the other side," she said.
If she makes it, she will then bike 3,000 miles from the west coast of Canada to Nova Scotia before returning to London over the North Atlantic.
A British adventurer has resumed her around-the-world journey in Japan after a tropical storm forced her to abandon the challenge last year.