TOKYO — Prime Minister Shinzo Abe is likely to move a step closer to his dream of becoming Japan’s longest-serving prime minister, with his party heavily favored to win a parliamentary election on Sunday.

For a clue to that likely win, consider Ko Watanabe, 25, a newly minted software engineer in Tokyo.

Mr. Watanabe is not quite sure what Mr. Abe means when he talks about revising the country’s pacifist Constitution. With family from Hiroshima and a great-grandfather who survived the atomic bombing there, Mr. Watanabe does not support Mr. Abe’s plan to restart nuclear plants idled since a devastating earthquake and tsunami caused the Fukushima nuclear plant meltdown in 2011. He does not believe Mr. Abe’s Liberal Democratic Party has been transparent about a possible shortfall in the nation’s pension system.

Yet come Sunday, Mr. Watanabe plans to vote for the right-leaning Liberal Democrats, as he has done since he was old enough to go to the polls.

Mr. Watanabe, on a lunch break downstairs from his office in a fashionable building in the Tokyo neighborhood of Shibuya, said he was just choosing the most secure option among a lackluster bunch.