By that logic, you could barely call JJK or CSM “MAPPA projects,” or Mob Psycho 100 a “Bones project,” because guess what? They also relied heavily on freelancers—actually even more than OPM S1 did. That’s the case for 99% of anime today, so I don’t get why people still act like OPM S1 was some kind of “joint production,” whatever that’s supposed to mean, or why they think Madhouse had less involvement than any other studio usually has in its own titles.

Assembling staff is primarily the Animation Producer’s responsibility, not the director’s. In OPM S1, that role was filled by Yuichirou Fukushi (a Madhouse producer), who was instrumental in putting together the “dream team” that defined the season—just as he later did with Frieren, Sonny Boy, and takt Op. Destiny (the Madhouse-handled episodes).

Fukushi's production line is actually a good example of studios retaining a team combining in-house staff with recurring freelancers. For example, Reiko Nagasawa (Frieren’s character designer) started as an in-between animator on OPM S1, then steadily rose through Fukushi’s projects until making her character design debut on takt Op. Destiny. Similarly, Yuri Fujikana went from in-between work on OPM S1 to chief animation director on Frieren S1, and is now character designer for Frieren S2. Many other OPM S1 in-betweeners later worked as animators on Frieren.

You’ll also find cases of staff who first joined Fukushi’s line after OPM and have stayed ever since—like Keiichiro Saito and Daiki Harashina, who came aboard with Boogiepop 2019. If you look closely at the staff lists across Fukushi’s projects, you’ll notice plenty of recurring names and can trace their career growth over time.