DAKAICHI -I'm being harassed by the sexiest man of the year-

Shion and Rui are the dream team when it comes to hitting on women. Tonight was going to be another night of hooking up with girls for Shion, but he ended up taking a strange drug. When he woke up... he'd turned into a girl?! Rui came looking for Shion, but didn't recognize him, and started hitting on him...

Kaoru is a college boy with everything going for him. He lives in a mansion with his beautiful fiancé, Aoi, all his roommates are babes, and they all have the hots for him. There’s just one hitch: due to family complications, Kaoru and his beloved have to keep their engagement a secret. As he gets tangled in countless steamy situations, can Kaoru overcome temptation and stay true to the lovely Aoi?

Izumi was born in a family of celebrities. His father is a singer, his mother an artist, his older brother the lead vocalist for the popular band CRUSHERZ. Izumi himself, however, is just a nerdy college student. He loves the manga "Magical Girl Lala Lulu" and dreams of becoming a manga writer himself. One day he is roped into filming a commercial where he wears a dress. Another actor on the set, Ryōma Ichijō, mistakes him for a woman and falls in love at first sight. As it turns out, though, they met ten years in the past. And Ryōma's feelings don't change when he finds out Izumi is a boy.

Despite their distinctive personalities, Souma Shiki, Hayate Ichikura, Shun Futami, and Takayuki Mima all have one thing in common: though naturally clumsy, the four disguise their embarrassment from tiny slip-ups by maintaining a composed demeanor. However, it is actually the guys' airheaded natures that makes the girls' hearts throb. No matter what happens in their daily lives, the boys do their best not to lose their cool!

First-year Toono transfers from Tokyo to the all-boys boarding school deep in the mountains, "Mori Moori Private School." The friendly Yaguchi who calls out to him becomes his only friend, but his dislike of sports makes him join the most laid-back looking photography club instead of Yaguchi's soccer club. However, the photography club is in name only and is actually nicknamed the "Yarichin Bitch Club," filled with colorful seniors. In contrast to the troubled Toono, Kajima, who joined the club at the same time, is completely unphased and even slips a confession to Toono into the confusion. Toono himself thinks Yaguchi is cute, but Yaguchi finds himself blushing around Kajima and stuff happens. Furthermore, complications arise between the seniors…

Kinoshita Kazuya is a 20-year-old failure of a college student. He managed to kiss his girlfriend once, but was dumped after a month. Completely spiteful, Kazuya uses a certain method to date a girl. He goes to their meeting place and a beautiful girl brushing her long, black hair behind her ear was there, smiling at him. Her name was Mizuhara Chizuru. Something real is born after just a single rental! A reckless rom-com filled with love and excitement is about to begin!

While spending summer with his mother, Haru meets Ren, a boy newly adopted by his mother. Getting along with Ren isn't easy as Haru's goal is to "civilize" him by the time summer ends. Their relationship slowly improves as Haru spends more time with Ren and in return Ren steadily warms up to him. Can they really become a "family" at the end of summer?!

After a shy office worker unexpectedly gains the ability to read minds, he discovers that his handsome colleague can't stop thinking about him!

There isn't a single person in Sakuradamon High who hasn't heard the legends about Seiji "The Mad Dog" Sawamura's demonically powerful right hand. His reputation makes it fairly difficult for him to approach girls, and after being rejected 20 times straight, he half-jokingly vows to finish high school with his right hand for a girlfriend. Much to his surprise, after waking up the next morning, Seiji discovers that his demon right hand has mysteriously turned into a miniature girl, Midori Kasugano, who reveals that she has had a crush on Seiji for the past three years. Because their situation is not ideal for either of them, Seiji attempts to return Midori to normal. But after causing a big misunderstanding at the Kasugano household, the pair decide to keep their predicament between them until a solution is found. Thus begins an odd relationship, and what could be the only chance for Midori to finally be with the one she loves.

Sekaiichi Hatsukoi follows three couples that are interconnected within the manga industry, with each being subject to the budding of first love.

Three couples, three intense romances: a student’s tutor crosses the line, a loner meets a force of nature, and a carefree man faces love he can’t ignore.

Kouyou Kotesashi, a sports doctor with massage skills, enrolls at Seiwa University Affiliated High School to secure a scholarship. He works as a live-in dorm manager, managing the school's talented female athletes and managing their well-being through intense training and massage therapy.