The former Bochum man scored in a third straight match as surprising Frankfurt remained unbeaten despite falling behind in the first half to the reigning Bundesliga champions
Shinji Kagawa's former team-mate at Cerezo Osaka contributed one goal and one assist to extend his scoring streak to three matches.
"It's good that we were able to catch up after we fell behind," Inui told reporters. "After our manager talked to us at halftime we all loosened up and were able to fight back"
"The two goals we gave up in the first half were unnecessary, but you could definitely feel their strength as champions and that was good for us to experience.
Down 2-0 after 45 minutes, Frankfurt fought back in the opening stages of the second half. Inui set up Stefan Aigner's goal in the 49th minute, before Aigner returned the favor just two minutes later with a cross that the Japanese headed in to equalise.
"[Aigner] sent a good cross," Inui reflected. "There were team-mates nearby so I was a bit nervous when I went up for the ball and it didn't look very cool, but it was my first header goal so I'll always remember it.
"I was exhausted at the end of the match, but since I stayed in I wanted to score the winner. But for us it's big to not lose this sort of match."
Undefeated Frankurt hope to continue their run when they host Freiburg on Sunday.