Based on the manga by Hiyo Hiyo.
Princess Cecelia was kidnapped by a witch, Etruria, and she was confined into the tower. The king proposed that if someone would save her from the witch he would let her marry him. A knight named Albion accepted the proposition. Whether would Albion beat the monsters living in the tower to get the top of the tower where the princess was confined? What would become of Princess Cecelia and Knight Albion?
Source: AnimeNfo

Endou Sakimi, a student, finds herself in a pinch. Having been betrayed by her previous boyfriend, she finds herself in incredible amounts of debt. She turns desperate, and seeks help from a man who runs a “gentleman’s service”, who confines her to a room 24/7, only allowing her out to perform her tasks. In there, she discovers Fujidou Mana, a mysterious young girl. Sakimi seeks to break the bonds placed on her, and free her and Mana from this hellish world of sexual desires and cosplay perversions.

Yuuichi Mamiya uses a penlight’s powerful hypnotic properties on his loving mother-in-law and younger sisters-in-law, amplifying their sexual desire. However news of the things that happen in the Mamiya household starts making trouble in the neighborhood. The president of the neighborhood association comes to talk with the Mamiyas, but she soon falls to Yuuichi’s hypnosis. Rumors about the Mamiya household spread throughout town, and Yuuichi is forced to take drastic measures.

Standing in for her daughter to take care of her son-in-law’s extensive needs, she finds herself getting a little too accustomed to this whole situation…

Another tale in the Milk Junkies series about two busty female characters interacting with a male protagonist.
Hayami Kouta is the superintendent at an apartment building, where two busty and very horny housewives reside. Whenever the ladies are feeling particularly unsatisfied with their husbands, they call upon Kouta for some personalized handywork. Thinking he’s making mere service calls, Kouta innocently arrives at the ladies’ apartments. But it doesn’t take long for Kouta to catch on that it’s the ladies that require the maintenance. Fortunately for Kouta, he’s got the right tools for the job.

Suzuna is a young miko (Shintō priestess) who lives in a mansion in rural Japan, and who is in training for a forthcoming great rite. A marriage has been arranged for her, and her fiancé is brought to her home, much to her dismay. But the mansion may be haunted, and a strange curse seems to take possession of its inhabitants…

Somehow without my realizing, the girl I liked for all those years had become a man-eating sexpot.
Summer vacation.
Ordinary protagonist Youta (virgin) found himself making out with his childhood friend Rio (non-vigin)…
“Do you like doing it with me…? I’ll take it off for you…”
Youta was bewildered. It was his first time, but certainly not hers. He put himself in her capable hands.

Sex with your childhood Final Fantasy girl.. check.
Dodge lawsuit from Square by changing a character in her name.. check, and check.
“Yufin” the self-proclaimed treasure hunter in 3.5 erotic episodes.