"To make it (a break of 100) sustainable, you need to see strong evidence that Japanese investors are buying rather than selling overseas assets, or you need to see a shift in hedging behavior ... But at the moment we don't see that from capital flows data."
(Read More: Japanese Banks Say Hola, Go Local as They Woo Overseas Borrowers)
One-month implied volatility on dollar/yen jumped as high as 14.415, a level not seen in two years, underscoring increased demand for options to protect against yen weakness.
Data on Friday showed currency speculators raised their bets against the yen in the week ended April 16, while lifting positions in favor of the U.S. dollar.
The yen has weakened 23 percent against the dollar since mid-November, when Shinzo Abe, who became Prime Minister in December, promised bold monetary and fiscal expansionary policies during his election campaign.
The euro also remained vulnerable against the dollar on central bank expectations. The single currency last traded down 0.1 percent to $1.3062.
Technical analysts at SEB said that a break below $1.3026 would likely "trigger a new round of selling" in the euro, with the next support then seen at $1.3001.
From a fundamental point of view, the euro has been hamstrung by persistent talk of an interest rate cut by the European Central Bank.
The euro "is moving toward 1.30 this morning because more European Central Bank officials sound like they support the idea of a rate cut or some form of additional easing from the central bank," said Kathy Lien, managing director at BK Asset Management in New York.
That makes this week's euro zone PMI and German IFO reports key, Lien added.
Even the re-election of Italy's president offered little support to the single currency, analysts said.
(Read More: Hollow Victory for Italy as More Turmoil Looms)
"Quite frankly, I don't think removing this uncertainty from the equation will necessarily translate into a euro positive ... as it means that there's yet to be resolution to the hung parliament," said Christopher Vecchio, currency analyst at DailyFX.