Will it be third time's a charm for dollar-yen?

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The dollar-yen has surged past 100 for the third time this year amid expectations that a win by Prime Minister Shinzo Abe's ruling Liberal Democrat Party at Sunday's upper house elections would bolster the government's power to push its radical agenda forward.

And analysts say the latest move past the key psychological level is a sign that prolonged yen weakness is here to stay.

The currency pair breached the 100 level on Thursday to trade as high as 100.86 and hovered around the 100-mark for most of Asia's trading session on Friday. Dollar-yen crossed the 100 target the first time since 2008 back in May, and tested the level again in early July.

"Dynamics [driving the yen] are a sign that markets are increasingly confident of a Liberal Democrat Party victory at the upper house elections," said Vishnu Varathan, market economist at Mizuho Corporate bank.

(Read More: What Sunday's Japan election means for Abenomics)

"The significance of a LDP majority in the upper house is that 'Abenomics' will have fewer impediments, which in turn should boost equities and soften the yen," he added, referring to the radical plan unveiled by Abe to kickstart the economy.

Indeed, the dramatic weakness in the yen, which has fallen 15 percent against the dollar so far this year, has been attributed to the three-pronged strategy behind Abenomics, involving monetary stimulus, fiscal spending and structural reforms.

While the government has delivered on the first two, successful implementation of structural reforms can only happen once Abe takes control of the upper house of parliament.

(Read More: Abe fires 'third arrow', but will it work?)

Some analysts have argued that the reason dollar-yen has not been able to sustain a strong move past 100 to the dollar is because Japanese investors have shown reluctance to invest abroad.

But that could be changing. Weekly data from the Ministry of Finance on Friday showed Japanese investors had bought the highest level of foreign bonds since September 2012.

Local investors bought 1.106 trillion's yens worth of foreign bonds ($11 billion) in the week ending July 12, the second week of net selling, after last week's purchase of 974 billion's worth of foreign bonds.

Kathy Lien, managing director of BK Asset Management, said she was watching this weekly data from the MoF as a key indicator of further yen weakness.

"[Increased Japanese buying of foreign bonds] is a trend that would be extremely supportive of dollar-yen," said Lien.

(Read More: Fate of yen hinges on Japan's weekend elections)

However, other analysts pointed to the fact that external factors, outside of Japan, were still a threat to the yen's weakening trend.

John Vail, head of global strategy at Nikko Asset Management, expects the yen to weaken to 103 to the dollar by December, but said the currency continues to be driven more by external factors, rather than political or economic factors at home.

"The yen still acts like a safe haven currency a little sometimes, but then at times it doesn't. It's hard to predict anymore how the yen will react to upsets in the market," he added.

Worries over the U.S. Federal Reserve tapering its stream of easy money revived the yen's status as a safe haven currency in recent months as investors moved in as they fretted over what the implications would be for the global economy, prompting some strength.

(Read More: Why the Hype Over Dollar-Yen at 100 Is Overdone)

—By CNBC's Katie Holliday. Follow her on Twitter: @hollidaykatie