Akihito, 83, expressed a desire in August to abdicate after nearly three decades on the Chrysanthemum Throne, citing his advancing age and weakening health.
Major national newspapers - the Yomiuri, Asahi, Mainichi and Nikkei - cited unnamed sources as saying Crown Prince Naruhito, 56, would succeed his father on New Year's Day 2019.
After Akihito's announcement last year, the government set up a panel of experts to help decide how best to proceed on an issue fraught with historical and legal challenges.
Though abdications have occurred in Japan's long imperial history there has not been one for 200 years. Under current laws there is no legal mechanism for one.
The six-member panel has discussed various legal options, with speculation rampant it will propose parliament pass a special one-time law to allow Akihito to step down.
The Democratic Party, however, opposes a one-time change, arguing this would not ensure stable future successions. It wants change to the permanent law that governs the imperial family.