"I have contributed in both friendlies. It is important to follow up each match. I contributed to the national team and I can contribute more," Kaka told Globo post match.
Neymar converted a penalty kick in the 25th minute and struck a left-footed shot from close range off a corner in the 48th to lead Brazil. Kaka scored following a breakaway in the 76th and defensive midfielder Paulinho had opened the scoring with a shot from outside the area in the 13th.
The win helps ease some of the pressure on Brazil coach Mano Menezes, who has been heavily criticized back home because of the team's disappointing performances recently. Brazil trounced weaker teams such as China and Iraq, but struggled against more traditional nations like Argentina.
Japan was trying to come up with another surprising result following its 1-0 win at France on Friday.
Marcelo, who missed action because of a fracture in the metatarsal of his right foot said he will "do everything right to return quickly and play with the team."
Brazil controlled the match and created most of the scoring opportunities, hitting the post once in each half.
"We had possession of the ball and created difficulties for their defense, we did just what we had to do," Menezes said. "We are putting a team together and it's important that now we are being able to repeat this team more often."
Brazil was coming off a 6-0 thrashing over Iraq in a friendly in Sweden on Thursday, but the victory against a stronger Japan team will do more to help Menezes fend off the critics who have been calling for his resignation ahead of next year's Confederations Cup and the 2014 World Cup that Brazil will host.
"The team deserves credit for this win," Menezes said. Brazil played well from the start and Paulinho put the team on the board with a right-footed low shot from the top of the area after a pass by Chelsea playmaker Oscar.
Neymar's goal from the penalty spot came after the referee called a controversial handball inside the area as Kaka tried to get past a defender, and the striker's second goal came from close range with a shot that deflected off a defender before going into the net. Kaka, who had scored against Iraq on his return to the national team for the first time since the 2010 World Cup, sealed the victory with a low shot after clearing a defender just inside the area.
Kaka struck the post with a low shot in the 35th and striker Hulk also hit the goal frame from a free kick in the 58th.
Brazil had a goal by Ramires disallowed in the 67th after the linesman said a cross by Neymar went out of bounds before reaching his teammate inside the area.
Brazil is not playing South American World Cup qualifiers because its spot in the tournament is guaranteed as host.
Information from The Associated Press was used in this report.