Ramandeep Singh (23rd, 37th) scored a brace in his comeback match after a long injury lay-off while Harmanpreet Singh (7th), Varun Kumar (14th), Hardik Singh (25th), Gursahibjit Singh (43rd) and Vivek Sagar Prasad (47) all got on to the scoresheet.
Japan sounded the board through Kenji Kitazato (2nd) and Kota Watanabe (20th).
India will face South Africa in Saturday's final while Japan will lock horns with the USA in the third place play-off match.
South Africa had earlier defeated USA 2-1 in the first semifinal.
Japan took the lead in the second minute from a counter attack with Kitazato turning in a pass from Kenta Tanaka from their first attack.
But India got their act together soon after, as Harmanpreet equalised from a second penalty corner.
Varun then beat the Japan defence with a powerful grounded flick to hand the hosts a 2-1 lead.
In the 20th minute, Japan scored their second goal from a counter-attack as Watanabe sounded the board after being set up by Kazuma Murata.
India restored their advantage three minutes later through Ramandeep, who scored his first goal for the country after returning from a year-long injury break.
Minutes later, India made it 4-2 when Hardik scored. There was no looking back from then on as Ramandeep scored his second goal of the day in the 37th minute while Gursahibjit and Vivek Sagar Prasad also netted from field efforts to register an emphatic win after the change of ends.
The FIH Series Finals provide two spots in the Olympic Qualifiers to be held in October-November this year.
( With inputs from IANS )