it's been slightly more than a year since Sato ren was changed into our mc ( by author) now. the news that war was immenent had reached even to the ears of civilians by now.
already many small skirmishes have happened with enemy villages troops near the borders and the numbers of spies routed from the leaf exceeded fifty. the number looked small but was more than enough to show the lack of security in leaf village .
the academy now abandoned the usual slow teaching patterns and practically forced students to graduate quickly. this forced many less talented children to grief in silence because they can only blame themselves for their lack of talent . the war was near so the village didnt have the leisure to guide each and every student properly and this fact all the children knew already.
the teachers in the academy were reluctant but they had no choice to select some better talented students to train with all their attention so that they can graduate and serve their part in the war as genins of konoha. well they were practically cannon fodder though .
the war was cruel on weak because simply even the kindest hokage cannot protect everybody from their deaths. the genin were used in bulk for dangerous missions regardless of the fact that they were complete newbies or not . even the chunin were no different but they still could lead small teams and make their own choices which could potentially save their lives on the chaotic battlefield. the village had no choice in this matter as whether they admit or not , a village's strenght is depicted by the number of jonin , elite jonin , S rank ninja or maybe kage level ninja . the rest were only potential not the current strenght so they were pretty much dispensable during emergency times like war.
sadly this was the cruel truth and most of the genin died on the battlefield everytime without even realizing that their beloved village had pretty much given up on them from the start . still some genin or chunin were lucky as they got much better treatment due to being students of veteran jonin or elite jonin of the village. for example team kakashi or team 7 etc .
when the village was in turmoil , 2 friends who were practically brothers now were undisturbed by this chaos and were training diligently daily . of course they both were dai and ren . dai was a simpleton already and ren had warned him about the possibility of war beforehand so he was carefree but increased the intensity of his training by one notch .
ren was as casual really busy as he trained in all types of combat whether it be ninjutsu, genjutsu, taijutsu etc . he even came up with original martial arts together with dai to enhance their abilities . but the area in which ren progressed the most was his pure body kenjutsu or swordsmanship as he didnt use chakra to either enhance his movements or weapons yet . ren even though being a novice was progressing in swordsmanship at a an average pace because of his strong comprehension ability which was again boosted by sharingan . ren could easily see his flaws in movements with sharingan and correct them before they could hinder his progress in future. but after one day , his progress exploded as he discovered one method to increase the comprehension pace quickly and easily.
the main cause of this happy coincidence was again shadow clones . these clones even though they dissapeared after suffering some hits but still they could practice like the normal body including the physical skills to some extent as they would dispel after exhausting their bodies too .
ren simply used this to his advantage and ordered every shadow clone which were 100 in total to practice only flying slash which was only possible for ren to unleash one time before exhausting his energy . like that 100 clones dispelled after cleaving the ground in front them in halves while leaving deep cuts .
this seemingly pointless waste of shadow clones was actually the genius idea which increased the comprehension speed explosively. flying slash was actually not a final move as one could use it many times after they master complete control over their body and its energy . ren could only produce one desperate slash simply because he didnt have any foundation of sword skills thus wasting most of the energy while performing the beautiful slash . the proof was the cut that was left by his slash . it may appear sharp but actually the sharpness was minimal or maybe even lesser . the ground or the area forward was destroyed unevenly by the unstable shot of energy . the ground simply was sliced a little because the weapon ren was using was a sword this the ground was only slashed in half for meager 2 or 3 meters in length.
originally the flying slash should travel at least more than 50 meters forward even though it was only basic level simply because ren put that much strenght in the attack . the trees or whatever was forward was not cut but only destroyed which was the proof of unstable strength behind the seemingly perfect attack.
so ren just ordered every clone to activate sharingan all the time and continue observing their own muscle movements all the time during performing the slash . the result was that the clones dissapeared after producing the slash but ren got 100 times the data which showed the distribution ( flawed ) of strenght during the attack movements.
so all the job left for ren was to continue collecting more flawed data while contemplating and solving those flaws slowly . this way even though ren only had basic knowledge of swordsmanship inside his mind , he was able to discern the flaws more easily as he didnt know any complicated stuff and only the basics which were most important foundation of kenjutsu or any martial art . thus ren's comprehension of sword improved explosively over this time frame as you can imagine how many clones he would have used for this stuff in these months everyday. and this was ren we were talking about who cannot exhaust chakra. still it's not like ren suddenly became a master swordsman or anything because this method of using clones also had a big demerit .
simply everytime ren would experience 100 times the fatigue of him exhausting all his body strenght after his 100 clones dispelled . so the mental strain was too much for even ren who had stronger soul . thus ren had to sleep or meditate for at least an hour evrtime to recover his mental power and then slowly erase the flaws in the control and distribution of strenght which took a long time as ren was a novice and the information from 100 clones was each different and too much . but after some months the progress exploded as the flaws became less and less while ren's control on his body strenght became better and better. after that ren started focusing on his kata and swings too again repeating the same process of dispelling clones after observing the muscle movements with sharingan while still perfecting his flying slash .
in the end now ren has improved too much and can effortlessly use flying slash and basic swordsmanship . but the good thing was his energy drain each time was minimal due to possessing almost no flaws in his kata , swing or technique .
now to further improve the power of his sword ren had to increase his body strenght, invent good sword skills or meditate to increase his sword comprehension slowly to sharpen his will or intent thus his attacks becoming passively more sharper and destructive . all in all this huge job didnt need ren to compromise his other skills practice like chakra control, fuinjutsu , ninjutsu etc..
during these months ren only used 10 clones to practice fuinjutsu while all his other more than 150 clones ( after a period of time) were busy with swordsmanship skills.
despite this much progress ren cannot bring himself to rejoice or even smile because his fuinjutsu teacher miko uzumaki has passed away now and it has been a few days since then too . ren didnt practice or couldn't motivate himself to practice these few days as his mood was down . what can you expect? after all even though ren can be considered a training maniac , he is still a normal earthling inside . he is not like ninja who have gotten used to deaths of their loved ones nor he will get used to it in future either.