No. The official Totoro franchise is known for its positive and heartwarming stories. The 'Totoro Dark Story' is likely just a fan - created or alternative interpretation that has no official standing within the franchise.
There were a few Japanese animes that involved elements of shadow combat. One of them was Blue Dragon, which was broadcasted on television around 2000. The protagonist was a teenager who could summon a shadow to fight through a device on his right hand, but the shadow seemed to only appear on the wall behind the protagonist. There was also an animation called Saint Robin, which was broadcast between 1989 and 1990. The protagonist could control shadows to fight enemies. In addition, the shadow ninjutsu used by the Nara clan in Naruto also involved the elements of shadow combat. Other than that, the other search results did not mention the specific name of the animation or related information.
One of the novels that matched the description was " Fairy Dragon Girl." The female lead of the novel was named Chu Yue, and she had a pet that looked like a Totoro. Chu Yue was a dragon trainer. She trained all kinds of dragon girls, including the big demon dragon. In this novel, the female protagonist's pet dragon had intended to eat her Totoro.
A normal Totoro story focuses on the magic and wonder that Totoro brings to the children's lives. However, a scary Totoro story often plays on our fears of the unknown. Totoro in a scary story could have hidden motives or be a symbol of something more sinister. The mood is completely different. In a normal story, it's warm and fuzzy, while in a scary story, it's tense and full of dread. There could be elements of the supernatural that are not so positive, like Totoro being a spirit that is angry or vengeful.
Cute Japanese cartoon art often features big eyes, colorful hair, and simple but charming designs. The characters are usually depicted with a sweet and innocent expression.