My memory of this manga is fuzzy because I read it a few years ago, but this was a very poor choice for a short story adaptation on Gou Tanabe's part; The outsider, a horror story by H.P. Lovecraft that predates the Cthulhu mythos, was really written specifically for the first person short story format. The story involves a man who has long dwelled in a decrepit castle with no understanding of the outside world or seemingly any concrete memories. He is trapped inside and seeks to escape. In Tanabe's adaptation, the man is shown in silhouette until the end reveal, which is very awkwardand unnatural. The twist provided by Lovecraft is less expected because the medium could conceal the nature of the main character without any strangeness...

Even in the roundabout way I've written the previous paragraph, the twist can easily be surmised. In the original story, though, it's the anxiety and despair that comes from the revelation to the main character more so than the reader that makes it effective, and this story remains a perfect counterpoint to Lovecraft's later cosmic horror with his usual academic-minded protagonists who had no choice but to resign themselves and humanity to whatever fate the cosmic pantheon of ancient and maleficent gods might choose for them.