Lower House lawmaker Kenji Eda on Monday deserted Your Party, which he helped form four years ago, and took more than a third of the opposition group's ranks with him to launch a new party.
The breakup of Your Party underscored the worsening turmoil in the opposition camp, which is being trampled by the ruling coalition led by the Liberal Democratic Party.
"We will go back to the origin of Your Party," said Eda, referring to the group's initial call for political realignment as a brand new third force. "The mission of the opposition camp is not to fight each other but to iron out differences over principles to offer an alternative that can counter the LDP."