I have been noticing that there have been highly lack of proper training methods of yin nature chakra though for yang we have medical jutsu practice which can with enough training led to great Manupilation of yang element like tsunade fir example she continuously use yang nature chakra to remain young as yang element is also called physical energy we can easily say that mastering yang nature can lead one to control all physical expect of body like - Age Manupilation , Gigantification(Akamichi clan), biofeedback (we have also seen biofeedback in one peice during cp9 arc) etc thus master of yang nature could become immortal likely
Now its come to yin nature also know as spiritual energy, sage of six path was one of the greatest master of yin nature such that even after 1000 of year after his death he could manifest his soul in elemental nation.(continent in Naruto world). But all we know that yin nature have only been used as genjutsu majority of time or certain jutsu like shadow Manupilation but what we have often been tell yin nature chakra depend upon our imagination but, like for wind nature chakra we have to cut leaf in two(see naruto practice with kakashi and yamato) or for fire burn leaf or earth crumble leaf or for water wet the leaf but for yin nature we have no clue to improve our control over yin nature element but I come to think as we know yin nature depend upon imagination we could alway imagine hardening of leaf while flowing chakra mean while also making it sharp this will gave manisfestion sign on leaf while practicing similar to wind element exercise in which person has to imagine cutting leaf in two.
I was just sitting and read novel i read about a person using spiritual energy to harden a paper use them as throwing weapon this gave me idea fir this as we all know yin nature chakra also represent spiritual energy which depend upon our mind and imagination .
so guy please do tell me if you find anything wrong in here . I expect fanfiction writer to freely use my idea I dont have any problem with them.