The Japanese attacker, who missed most of the second-half of last season, was delighted to be on the scoresheet as BVB claimed consecutive Bundesliga titles
Kagawa, who missed most of the second-half of last season through injury, netted Dortmund's second on 59 minutes to seal the victory and back-to-back titles.
"I'm feeling a lot of emotions, and I really do feel a sense of completion," Kagawa told reporters after the victory.
"Even though we had a really difficult period, we were able to win the championship and it's because of how close we all were. I really want to thank my team-mates and the fans. This wasn't something I could have ever accomplished alone, and it's amazing."
The 23-year-old said he was delighted to have scored a crucial goal in the decisive game.
"To score a goal like that as we were closing in on winning the championship and guarantee the result was really incredible," he said.
After for his overall performance in the game, Kagawa said he felt he played better in the second 45 as he was able to find space.
"I had a bit of room to work in. In the first half I didn't feel like I had room when I was moving, but in the second half I really felt like I did," he said.
"Our opponents stopped pressuring us. In a late season game like this it's hard for our opponents to stay motivated. But we were motivated by the opportunity to win the championship, and so we were able to create many chances."
When asked if there was a turning point in the season, Kagawa opted to praise the team's consistency over the course of the whole season.
"I don't think there was one (turning point). We fought hard in every match of the second half of the season," he said.
"As a team we were able to perform well in all aspects. The results of our hard work showed in the second half, so it was a wonderful year."