Just so there are no confusion: This doujinshi is semi-canon. The original ending of Inuyasha never happened: Naraku has not been defeated and they are still looking for all the jewel shards. There is no set point or chapter where this doujinshi picks up from the manga but just know that as of right now, Sesshomaru still only has one arm. Other than that, despite the fact that they are still hunting for jewel shards and all that goodies, it has been a few years so Kagome is around 17-18 years of age (which is why she's in her high school uniform (canon) instead of her middle school one).
Sesshomaru and Kagome ---> Rumiko Takahashi