Well, it's hard to say for sure. Sometimes a Touhou comic might stick closely to certain expectations, while in other cases it could take some creative liberties and deviate.
In my opinion, the story of Flandre Scarlet is also a great one in the Touhou series. Flandre is a powerful vampire who has been locked away for a long time. Her story is about her isolation, her struggle with her own power, and her attempts to interact with the outside world. It shows her complex personality, from her child - like innocence to her terrifying strength when provoked. This contrast makes her story very engaging.
Well, start by familiarizing yourself with the Touhou characters and their backstories. Then, plan out a simple storyline that fits the Touhou universe.