was a Japanese politician. He was a leader of the Democratic Party for the People (DPP) and the Democratic Party (DP). A native of Nagoya, Aichi, he attended Waseda University and received a Ph.D. in fiscal and monetary policies and reforms. Afterwards, he worked at the Bank of Japan from 1983 to 2000 before being elected to the House of Councillors for the first time in 2001.
After the 2017 general election, then-Democratic Party president Seiji Maehara faced intense criticism for his decision to disband the DP caucus in the Lower House and forcing DP members to seek re-election as members of Kibà  no Tà Â, the CDP or as independents. As a result, Maehara resigned as DP president on 30 October 2017. Otsuka was elected unopposed to succeed Maehara the following day.
In May 2018, Otsuka led the DP to merge with Kibà  no Tà Â, forming the DPFP. Otsuka became the co-leader of the new party, along with Kibà  leader Yuichiro Tamaki. He chose not to run for a full 3-year term in the DPP leadership election in September 2018.
He stated his intent to leave the party in 2024, citing his desire to run for mayor of Nagoya. This came after Seiji Maehara and a group of others defected from the DPP due to party leader Yuichiro Tamaki's ambivalent stance on if he wished to join the LDP government or continue as an opposition member.
Otsuka died from heart failure on 2 March 2026, at the age of 66.