Kanojo no Kagi wo Akeru Houhou

A new series by Yumi Nakata, author of Chu-Bra, with yet another focus on underwear. Or rather, not wearing underwear.

Haruma's first impression of Chitose would be striped panties. Running into her in the hallway, Chitose's panties greet Haruma before they even know each other.

Immediately, Haruma finds himself attracted to this mysterious striped pantied girl, only to discover that she is transferring into his class AND she is going to be the housekeeper at the apartment complex his Grandfather owns -- due in no small part to his grandfather buying up her debt (leaving her in indentured servitude to the apartment complex until she pays it off).

Thus starts Haruma and Chitose's growing relationship, which is hampered only slightly by the fact that Chitose is a raging exhibitionist, barely able to keep her panties on for any significant length of time. Er, what?

Let the skirt flying romance comedy begin!

Tropes used in Kanojo no Kagi wo Akeru Houhou include:

Accidental Pervert: Chitose, in a rare female example. Part of it is caused by her tendency to lose her underwear, and her mild tendency towards exhibitionism.
A Date with Rosie Palms: Chitose during the "climax" of Chapter 1. She takes off her panties due to them being too damp to wear after her and Haruma's Meet Cute, then the act of running away (and up the stairs) from Haruma gets her even more wound up, and the realization of the feeling of going around commando (as well as the realization that anyone on the ground could look up and see under her skirt) is finally too much for her. (Worse, as we discover on the last page, she never did bother putting her panties back on.)
- Even more, her thought bubbles afterwords suggests this is a regular occurrence for her.
Book Ends: The first chapter begins and ends with Haruma making a joke about Chitose's name.

Haruma: If you pair the words 'Striped Panties' with 'Transfer Student', it becomes Hayamine Chitose.
Haruma: ... If you take off 'Striped Panties' from 'Transfer Student', it becomes Hayamine Chitose.

Dojikko: Chitose, played completely straight. If she ever walks or runs away, a chibi version of her will be seen falling down in the next panel.
Gag Boobs: The class rep. Her gainaxing is overstated as a gag during the maid uniform chapter.
Going Commando: Chitose, constantly. She's even holding her panties on the cover of the manga.
Hadaka Apron: In Chapter 7, Chitose sees her lookalike wearing hadaka apron in the ero-magazine Haruma obtained. This inspires her to try it herself, since she was alone while Haruma was out shopping. Which is exactly when Haruma comes back. Before anything can come of it, Sayuri visits.
In Vino Veritas: During her welcoming (drinking) party, the sight of the class rep getting drunk and being teased by Sayuri... or rather the site of Haruma drooling over it... causes Chitose to take her panties off and place them on Haruma's head.
Meet Cute: The first shot of the story. Haruma runs into Chitose, getting a glance of Chitose's striped panties. She reacts poorly, but not for the obvious reason. She was embarrassed that having her panties seen turned her on.
Meido: The class rep in chapter 6, made all the more fanservicey because she is very obviously not wearing a bra. Chitose follows suit, although she has to make it more obvious that she's not wearing one to Haruma.
Ms. Fanservice: Sayuri, who is a stripper by night. She walks around in the most sexual underwear she can during the day, because "it's her uniform." And because this is a Yumi Nakata manga.
Not So Different: The class rep wants to think she's above the shenanigans, but a pitcher of beer ends up causing her to all but become Sayuri's understudy.
Not What It Looks Like: The class rep falls onto Haruma, giving him some inadvertent Marshmallow Hell, which sends Chitose into the Corner of Woe.
Panty Shot: Repeated, mostly of Chitose. Sayuri's doesn't count, as she doesn't wear clothing other than fancy lace lingerie.
Potty Emergency: Chapter 5. Chitose and Haruma are locked in the nurse's room by Those Two Guys. Chitose has to go (for a few reasons) but can't leave the room. Haruma suggests various solutions (a discarded bottle, an empty plastic container), but Chitose rejects them and runs away... falling down in the process and causing her to have the beginnings of a Potty Failure.
- The Meet Cute in chapter one either ended with a Potty Failure or... a more illicit effect; either way Chitose's panties were too damp to wear for the rest of the day.
Reluctant Fanservice Girl: Chitose combines this with her exhibitionism to weird effect. She's constantly humiliated by the situations she finds herself in, especially in front of Haruma, but at the same time enjoys them on some level. Fortunately for her she's also a Tsundere, so personal epiphanies need not apply.
Right Behind Me: While practicing a pose in Hadaka Apron in Haruma's house, Chitose imagines the jawdropping look of shock he'd have if he walked in and saw her. Then she turns around and the jawdrop the very real Haruma is sporting is even bigger.
Shameless Fanservice Girl: Sayuri doesn't wear clothing, instead wearing the most elaborate underwear she can. She justifies this by saying she's a stripper and it's her uniform. (Haruma isn't buying it.)
Tsundere: Chitose to Haruma, partially because of the embarrassment her condition causes her (which Haruma keeps ending up involved in, one way or another).