Exactly what part of their abilities are taken away? I'm soo confused...is it any ability they aren't born naturally with? I remember in a future comic, Sakuya could use her power to stop time, and Satori's ability to read minds...but Reimu couldn't use her ability to fly! HOW DOES THIS WORK?! @_@
Basically, any energy they expend outside of their bodies is almost instantly dissipated. Thus, only powers that work within their bodies (Like Sakuya's contact-timestop) or their own natural abilities (Like Cirno's fairy ressurection, Utsuho's flying, Orin's cat-transformation) will really work.
Something that also works, and the reason why they were able to withstand Utsuho's Mega Flare inside the ring was they can use their energies *internally* with little to no hindrance. Thus, Reimu, Sanae, Sakuya, and Marisa being able to hold their own against the likes of Yuuka, Yuugi, Remilia, and Flandre despite being mere humans.
Apparently, you CAN have so much power you can overcome it (See Utsuho), and if it's not truly an energy ability it doesn't work quite the same. Flandre's Four of a Kind for instance, made four of her...but they were all her, and because she was expending four times the energy, she tired out very quickly, which leads to my own speculation.
Something I believe happens is that it also blocks the ability to 'recharge' themselves, meaning they're running on battery power during the matches. Outside of the ring, they're running on the mains, so they can recharge themselves. The more power they use in the ring, the faster they'll run out, and it won't be until after they leave when they can top off the tank, as it were.
*facefaultss* It's been a year and you guys STILL have missed on the G Gundam reference?
Shining, Grip, a hand glowing red, etc, etc...
The only powers we can use inside are the ones within ourselves.Pretty much.Us humans aren't like you, with your unlimited youkai strength.Just like money, holy power is all about economizing!You'll be inside the barrier from here on in.Yes, energy related to any sort of powers is mostly nullified.Yukari and Kanako really put a lot of work into this, huh?...if I disperse my holy power in here, it'd vanish in a blink.BarrierHmmm...I can't sense it at all...If she hadn't said something, I wouldn't have even noticed it.I'll bet...Kapa...*slight movement*Episode 128: Human's Power, Demon's PowerFrom the Artist's Pixiv pageThe only way for a human like me can stand up to the likes of you is...Huh, a clever way to use your powers.To heighten my holy powers within myself, and prevent them from escaping by setting up a thin barrier...*Shuuuuuuu*...
Sound of her power dissipating*grip**grip**shining*Alright!