Since rotary fans essentially "chop up" air as part of its function, speaking/breathing into a fan will cause a distortion effect on the voice.
Even if it's a recent production, anime and manga use the wire-cage-&-clear-blue-blade fans that haven't been sold in the US since the 1990's.note These fans are increasingly rare in Japan, too. But since most manga authors grew up in the '90s or earlier, they're still present in their works.
Note that you can achieve a similar vocal effect with a modern plastic fan. The old wire-frame ones are somehow more satisfying, though.
- In an M&M's ad announcing the return of Crispy M&Ms, Yellow does this by accident. (He'd misunderstood what Red meant by "tell our fans".)
- A radio ad for Geico motorcycle insurance has a woman sitting close to a fan in her office because she misses the feel of the open road on her cycle; all her dialogue has that sound.
- Lucky Star: Konata and Tsukasa do it. Kagami calls them out on it, but Kagami's father mentions that she does the same. note
- Happens in Hidamari Sketch, where Yuno and Miyako catch Sae talking into the fan, pretending to be an alien.
- Azumanga Daioh: Osaka does this while riding with Nyamo to Chiyo-chan's summer home.
- Kaguya Houraisan in the official Touhou Project yonkoma strip Inaba of the Moon and Inaba of the Earth. If you're wondering about the bunnygirl's reaction, they're from the Moon.
- Ritsu in Season 2 episode 11 of K-On!.
- Komori in Sayonara, Zetsubou-Sensei, explaining what she would do on days of privation.
- Nozomi does it in Mayoi Neko Overrun!. "Nya-a-a-a-a-a-a-a..."
- Yukito does this in an early episode of AIR.
- Bobobo-bo Bo-bobo once got second place in a contest for doing this.
- The Idolmaster: Hibiki does this once before the Beach Episode.
- Thermae Romae: After being transported to modern-day Japan, Lucius finds himself inexplicably compelled to do this.
- Nichijou: Yuuko is tempted into doing this, but cannot due to a label prohibiting it.
- In GO-GO Tamagotchi! episode 8a, Mimitchi brings a simple house fan as her entry to an invention project for robotics class, and everyone else has fun yelling "Ahhhhhhh" into the fan as it's blowing and hearing their voices being distorted by it.
- Tommy Boy: Luke... I am your father!
- Done by a giant, dementia-suffering grandfather in Big Man Japan... with an airplane's propeller.
- Rizzo and Pepe do this in Muppets from Space as part of a scheme to get Gonzo to build them a Jacuzzi.
- Shriek If You Know What I Did Last Friday the 13th: The Killer spoke through a fan to mimic Ghostface's voice modulator. Dawson and Martina find the fan when they search him (it's one of those end-table models that really has no hope of being portable).
- This is how the vocal effect on "I... AM... IRON MAN!" was achieved.
- Martha Speaks: Martha and TD do this at the start of "Martha Spins a Tale." Helen finds it irritating.