No, they aren't similar. The characters, settings, and plot developments in the two mangas are very different. 'Are You Human Too' is complex and futuristic, whereas 'Absolute Boyfriend' is more straightforward and emotional.
I'm not sure specifically as I haven't read it. But generally, it might be about the last remaining human in a post - apocalyptic world, or perhaps a world where humans are on the verge of extinction. It could explore themes like survival, loneliness, and the value of humanity.
The 'No Longer Human' manga is based on the novel, but it does make some adaptations to suit the medium of manga. It retains the core elements and essence of the story though.
It depends on personal preference. If you like visual storytelling, the manga might be more engaging as it shows the characters and scenes directly. But if you enjoy delving deep into a character's psyche through detailed text, the novel could be more appealing.
The medium - specific elements also play a role. The 'no longer human' novel uses only words to create the atmosphere, while the manga can use different art styles, shading, and paneling to set the mood. For instance, a dark and shadowy art style in the manga can enhance the sense of gloom and despair that the story often conveys, while in the novel, it's the language and the sequence of events that build up such emotions.