Despite being battered in Sunday’s election, the Constitutional Democratic Party remains Japan's top opposition party in the Upper House after a tough fight against rival Nippon Ishin no Kai, which gained seats and is the second-largest opposition party.

But any celebrations of relief, in the case of the CDP, or success, as with Nippon Ishin, may be subdued given the concerns both parties have regarding their future leadership.

Winning 17 seats, the CDP now has a total of 39 — down from the 45 it held before the election. One key victory for the party took place in Kyoto, where former CDP Secretary-General Tetsuro Fukuyama had faced a tough race against a Nippon Ishin candidate backed by Seiji Maehara, a former foreign minister and influential member of the Democratic Party for the People.