Yuuji Fujiwara had an unlucky life. As a child, he was blamed for a vase he did not break, and he was fired from his job for a colleague's mistake. At the convenience store where he works part-time, Takamiya, a younger girl, blames him for mistakes made by others. When he returns home in a depressed mood, he is greeted by a strange girl. When Yuuji is puzzled, the girl reveals her true identity. It turns out to be a mucus creature that has been living with him for the past three months. The creature, which speaks human language and can change its shape at will, is in love with Yuuji. Yuuji is not at all pleased with the mucus creature's affection. In order to attract Yuuji's attention, the mucus creature changes its shape into Takamiya, the co-worker at his part-time job, and seduces him. 
 
(Source: MediaBank, translated)

Yuji's an ordinary guy who just wants to live his life in peace. His girlfriend's an extraterrestrial slime... who just wants Yuji all to herself.
 
(Source: JList)
 
1-9. Doukyo Suru Neneki (同居する粘液); COMIC Unreal Vol. 72,73,75,77,78,79,81,82,84.
 10. Hedonic Nerve (ヘドニック・ナーブ); COMIC Unreal Vol. 70
 11. Residence: Shounen Shoushitsu 2 (レジデンス～少年消失2～); COMIC Unreal Vol. 71
 
Included One-shots:
 Doukyo Suru Neneki Melonbooks Tokuten Leaflet Neneki to Nichijou (同居する粘液 メロンブックス特典リーフレット 粘液と日常)