The story follows the relationship between two co-workers, office worker Rena Yukuhashi and businessman Ryouhei Hachiya. Yukuhashi seems like the plainest woman at her company, but she transforms into a stunning beauty when she dresses up outside the office. Flustered upon seeing Yukuhashi transformed, Hachiya inadvertently utters what sounds like an invitation to get to know each other better — without realizing they are standing in front of a love hotel. 
 
(Source: Anime News Network) 
 
Note: The complete edition with explicit scenes was distributed web via Comic Festa Anime Zone. The censored version was broadcasted on Tokyo MX.

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The usually quiet girl is moving her hips on her own... Asking me to go deeper... Letting me do whatever I want... This side of her only I know... I want to see more of it.
 
(Source: Coolmic)
 
Volume 1: Jimihen!!: Jimiko wo Kaechau Jun Isei Kouyuu (じみへんっ！！～地味子を変えちゃう純異性交遊～) 
Volume 2: Jimihen!!: Jimiko ga Torokeru Dekiai Seikou (じみへんっ！！～地味子がトロける溺愛性交～) 
Volume 3: Jimihen!!: Jimiko mo Midareru Zecchou Seikou (じみへんっ！！～地味子も乱れる絶頂性交～) 
Volume 4: Jimihen!!: Jimiko ni Himitsu no Haitoku Onsen (じみへんっ！！～地味子に秘密の背徳温泉～)
 
Notes: 
- Includes 4 extra chapters. 
- Originally serialized as a web manga under the title Jimiko wa Igai ni Erokatta (地味子は意外にエロかった). 
- Released in long-strip format and subsequently sold in traditional format.