A meditation techniques that ingrains the 'Soul of Ice' technique, into ones mind.
Reidoken is like a light switch. He wants it, he turns it on. He doesn’t need it, they turn it off. There is no 'control' to worry about. However while in the Soul of Ice state, his 'warm' emotions are literally held at bay like a dam holding back water. It for this reason that user shouldn't use it for extended periods of time, like during meditation. When you release the Soul of Ice, it's like a dam opening its floodgates. Now granted, during meditation your emotions don't grow and fester very much, so that's not so much a problem. However, when you meditate there's a chance of tapping deeply into your subconscious, where the Soul of Ice rests waiting for activation. You dip deep enough into that, and there's a chance of emotional contamination. Or personality blurring, you could call it. However this can be overcome with experience.
The trainee sits completely cross legged in a pool of ice water as they meditate on the soul of ice while their elder. Eventually the trainee is going to pass out however their consciousness will remain active. The best way to describe what will happen is a very vivid dream. During that time, they are provided the subliminal programming that will overtake their core personality. Given that they'll be in a dream while this is happening, the effects will likely be significant and frightening. It's important that they don't resist. As kousei ingrains the 'Soul of Ice' technique, into the trainees mind their vision will obviously have a winter theme however what that theme is; is entirely up to the trainee’s subconscious. What Kousei does is force the trainee to abandon their passionate and loving feelings; their “warm” emotions to prepare for the onset of the Soul of Ice. The stronger the feeling the greater its resistance eventually the trainee must destroy the strongest feelings of warmth themselves. When the ordeal is over the trainee will fully lose consciousness allowing their mind to rest.