Franz von Stresemann, often referred to by the nickname Milch, is an elderly German conductor with a world-renowned reputation who arrives at the Momogaoka Music Academy as a guest instructor. His background is that of a celebrated and highly respected figure in international classical music, yet his behavior upon arrival immediately contradicts this dignified image. He is an oddball lecher, a skirt-chaser whose antics include taking photographs of female students' underwear and frequently skipping his duties to frequent night clubs and hostess bars, a particular favorite being a place called One More Kiss. His love of alcohol is such that he becomes drunk easily, often leaving his young apprentice to clean up his messes. Despite his genius, his personal life is a mess of frivolous and perverted pursuits that constantly get those around him into trouble.

Stresemann's primary motivation for accepting the position at the academy is a personal favor; he has been passionately in love with the Academy's Director, Minako Momodaira, for many years and composed a song for her in the past. While the romantic aspect of this relationship has faded over time, it remains a thread in his connection to the school. Underneath his lecherous and unserious exterior, however, lies a musician of profound depth. He is driven by a genuine love for music and a keen eye for raw, unpolished talent. He immediately takes an interest in the eccentric pianist Megumi Noda, seeing in her a unique and special gift that others might overlook. His role in the story is that of a catalyst and a mentor, albeit an unconventional and often absent one. He is the one who forces the perfectionist prodigy Shinichi Chiaki out of his comfort zone, repeatedly rejecting Chiaki's applications to his conducting class before finally accepting him as his one and only apprentice. Stresemann does not teach through rigid instruction but through exposure and challenge, demonstrating how to feel and express music in a way that technique alone cannot achieve.

Key relationships define his function in the narrative. His relationship with Chiaki is central and complex. Stresemann's wild behavior and seemingly arbitrary demands constantly exasperate the serious young conductor, often forcing Chiaki to take over rehearsals as vice-conductor. However, these trials ultimately push Chiaki to grow, helping him overcome his insecurities and learn how to connect with an orchestra on a human level. For Nodame, Stresemann acts as an admiring yet detached patron, recognizing her prodigious abilities and using his influence to create opportunities for her. He later develops a fatherly-like affection for both Chiaki and Nodame, watching over their progress and offering crucial, if sometimes backhanded, support from the shadows. He also has an ongoing, petty rivalry with other legendary figures in the music world, such as Chiaki's former teacher Sebastiano Viera, though these conflicts are often revealed to be rooted in surprisingly trivial personal slights.

Despite his buffoonery, Stresemann demonstrates notable abilities that justify his reputation. When he chooses to conduct, he displays a magical touch, able to transform a faltering, nervous orchestra into a cohesive and inspired ensemble with simple gestures of encouragement and understanding. He hears not just the notes but the anxieties and ailments of the individual players, knowing exactly how to draw out their best performance. His lessons on conducting, while often delivered drunkenly or offhandedly, teach Chiaki about humor, respect, and the importance of nurturing the musicians as people, not just as performers. Throughout the story, he undergoes a subtle development, eventually being forcibly dragged back to Europe by his stern assistant Elise to resume his professional career, but his influence continues to be felt. He evolves from a chaotic agent of disruption to a genuine, if distant, benefactor who has shaped the futures of the two young protagonists.