Yuurei to Boku

Yamato, a high school student, is troubled by a recurring dream. In these dreams, mysterious tentacles do naughty things to him, which he finds increasingly pleasurable. The tentacles attack him wherever he goes, even during class or in the nurse's office... what is their true identity?

(Source: Fusion Product, translated)

Note: Includes the one-shot "Neko to Janken (ネコとじゃんけん)" and one extra chapter.