Herrmann (David Eigenberg) and Mouch (Christian Stolte) are two of the most beloved characters on Chicago Fire. They are the wiley veterans, the guys who can always be relied on to do their work and dispense helpful advice to the younger team.
Well, drama is waiting around the corner for these two in season 13. The best friends are going to be put in a situation where one of them may be forced out of Firehouse 51 in an effort to further one of their careers. Neither wants to go, which will invariably lead to some heated conversations.
Herrmann and Mouch are being considered for transfer

Chicago Fire showrunner Andrea Newman confirmed this revelation during a recent chat with TV Insider. She noted that Herrmann and Mouch are both at a point where their rank makes it tough for them to co-exist under the same roof as Kelly Severide (Taylor Kinney) and Stella Kidd (Miranda Rae Mayo).
There's only so many high ranking positions in one firehouse, so the solution would be to send one of these veterans elsewhere so they can lead a less experienced team. Things get complicated further by the involvement of Chief Dom Pascal (Dermot Mulroney). Pascal is in charge of 51, but upcoming events will make his ties to the firehouse tenuous as well. Somebody will have to go.
"This is such a fun and intriguing triangle," Newman explained. "Everyone has different desires, skills, relationships — and Pascal, Herrmann, and Mouch are all heading full speed towards the end, where only two seats will be available." The showrunner made it clear that this will not be a case where an easy solution is discovered, and all three men will get to stay out. This is a problem that will case an enormous 51 shake up.
Mouch argued with Chief Pascal about his future

O"ne of them will have to go, and they all know it," Newman promised. "So the game’s afoot." We saw the beginning of this conflict in the episode "Too Close." Pascal called Mouch into his office and set up the idea of Mouch transferring to another firehouse. Unsurprisingly, the character turned it down. He made it clear he wanted to stay at 51 with his friends, which led to an intense back-and-forth.
Pascal has also tried to prime and mentor Herrmann for his eventual leadership role. He asked that Herrmann stand by his side and observe during the One Chicago crossover, but Herrmann ditched his post and demanded he be allowed to help when things got out of hand.
The smart money suggests Pascal will be the one forced to leave 51. That said, we don't know what the debate leading up to a transfer will do to Herrmann and Mouch's friendship moving forward. We hope they can get past it. Assuming, of course, they still work together when all is said and done.