The White Queen or The 100 Worlds. 18

Romance

Her whole life has changed in a moment when she said 'Yes'

Raiden-18

Action Comedy Seinen

Taking a break from her popular, brilliant, Fullmetal Alchemist; Arakawa-sensei drew up a one-chapter humorous Shounen story about a Frankenstein tournament, for mangazine GX to commerate their 5th year anniversary. (Source: Anime-Source)

18 Diary

Romance School Shoujo

1. 18diary 2. 17's Bible 3. Tadashii Hoshi no Miagekata

Durarara!! 18 Shiryaku

Action Drama Supernatural

A series of side stories that were bundled with the first press release of all 18 Blu-ray/DVD volumes of the 2nd season of the anime.

Ojamajo Doremi 18

Magic School

18-sai no Kodou

Shoujo

Another tender love story which fails to run smoothly from the master of such works Yukari Kawachi! This is a one volume "novel" type manga. Rui will be a model, and Tougo will be a painter—the two young childhood friends dream about their future. When Rui's father dies when she is 17, she goes to Tokyo, to fulfill her dreams—and meets a handsome make-up artist and...! (Source: Hidoi~! Translators)

18-sai no Himitsu

Romance School Shoujo

18-year-old Sako is tired of her loveless high school life. Her only comfort is her teacher whom she frequently visits for love advices. Now that her graduation is coming up, will she be able to seize the love that she has always wanted?

R-18 Love Report!

Romance School Shoujo

Riko Mitsumi is sixteen year-old girl who is pretty and a good student. She would be like most girls if she wasn't constantly dreaming about sex and using a pseudonym to write about it. (Source: M-U)

Nanami 18-sai Mama ni Narimashita

Yaoi

Nanami's older sister ran away from a member of a Japanese mafia; therefore, even though Nanami is only a 18-year-old boy, he has to be the mother of the baby and a captive.

18 Years Old, We Got Married

Shoujo

Life isn't that great when it's composed of a stubborn sister, single mom, and a dad that left you for someone else? If that's not enough, you meet a dwarf that's part of a famous boy band? Could this get any worse?! (Source: Within Silence)