|Spoiler Alert: This page contains spoilers. Read at your own risk.|
Perfect Diffusion (極致拡散) is a Convergence Type and Dispersion Type Magic that levels out the target area's gaseous, fluid, and physical energy distributions to the point of non detection. Normal Magicians can only use the weaker version, Diffusion, with difficulty. It's Kuroba Ayako's innate magical ability, also known as "Perfect Darkness".
Any gas or liquid that is distributed by physical energy is averaged out in a designated area, making it impossible to identify. The 'Decomposition' and the direction of the event modifications are similar in respect to the increasing depth by how the reduction of the identifiable area becomes. 
|“|| Ayako had a forte -- the unique magic [Perfect Diffusion], aka [PD (Perfect Darkness)]. A magic that leveled out the target area's gaseous, fluid, and physical energy distributions to the point of non-detection. Categorically [PD] belonged to convergence-type magic. Since it could be recorded into an activation sequence it means it was a normal magic. However, it was safe to say that ordinary magicians could only use [PD]'s weaker version [Diffusion] with difficulty. Tatsuya knew only Ayako could cast [PD].
For example, if sound is to be [leveled off], both voice and music will be totally leveled off into white noise where it's impossible to decode their meanings. However, the sound, in other words the generated sound itself, could not be hidden. This is still on the level of [Diffusion].
When a sound-deadening leveling-off zone has been spread out, the [Diffusion] magic finally becomes [PD]. Ayako's magic activation speed and interference strength were inferior compared to Miyuki's. However, she could spread out event interference zones larger than Miyuki's, and for this it was praised as the Yotsuba's greatest ability.
It's on dimly-lit outdoors at night where Ayako can fully unleash her specialty. She can selectively and instantaneously level off her own or her allies' reflection and emitted electromagnetic waves, melding into the darkness. By leveling off audio waves and air current variations, she can evade auditory and olfactory detection. And so she assimilated them into the night. Her code-name [Yoru] was based on one character of her first name, and at the same time it designated her unique perfect diffusion magic.