From MangaHelpers:

Shou lives out in the country. He has a big crush on his childhood friend Sora, but is afraid that she thinks of him only as a little brother. One day, Sora announces that she was abducted by aliens. Later that day, Shou confesses his feelings for her and she dies shortly afterward. Shou is still in shock from her loss, when an alien girl named Lila comes down from the sky. She has a disk that contains a brain scan of Sora, and she can run Sora's personality in her own body. She also wants to have a child with him. Will Shou be able to cope with all of these sudden changes, and will he be able to keep Sora with him after all? [tethysdust]

After both his parents died in an accident, Tsugawa Tatsuya is now left with millions of heritage he can't use. In the weeks after, he's still mourning and thinking about his father's last words, "Tsugawa family's man must be a man of great vessel". But Tatsuya is not confident he can fulfill his father's last wish.
One day, he met Miyazaki Seine, a strange girl who seems to enjoy being bullied. Tatsuya believes he can help her even though his friends only see her as a masochist pervert, and Seine herself told him to mind his own business.
Seine hunts creatures of the sea, a kind of parasitic bug that controls humans and influences them to do hateful things. She possesses an immortal body and a beast called AiON that's used to lure and devour the bugs from inside the human host. She and the bugs naturally have an impulse to kill each other on contact.
Even so, Tatsuya still can't just leave her alone, he wants to help her.

Hirose Goushi has a huge sister complex. So huge, he moves from his home town to Tokyo to attend Myouzen University in order to escape it!

Three years later, Goushi's little sister Noa shows up and informs him that she's taking the Myouzen University entrance exam and that she will be moving in if she passed. Little does Goushi know, she has a similarly large (if not larger) brother complex.

Read as Goushi attempts to hide his feelings for his sister, while she purposefully sets him up for failure.

From Tokyopop:
Volume 1:
Karin is a cute little girl who also happens to be a vampire...with a twist. Once a month, she experiences intense bleeding from her nose--we're talking gushers! In other words, she's a vamp with blood to spare, so rather than stealing blood from humans she actually gives her blood to them. If done right, this can be an extremely positive experience that benefits the "victim" as much as the vampire. The problem is that Karin never seems to do things right!

Long ago a magical cat disguised as a human woman fell in love with a human man. It is said that during their time together they even had children. They say that afterwards, the magical cat dwelt happily as a human, that she ascended to the heavens and became a cat-god, and is even now watching over the world of cats and men.

Of those descendants, the cats of Cat Forest Town say that they have mysterious powers. The townsfolk care for the cats as their guardian deities, and the cats, too, have become attached to the humans.

(Source: MU)

Koyoki goes to Tokyo and moves next door to the boy Shirahai that she liked in High school. When she went to visit, a girl greeted the door instead, Whom she thought was the boy's girlfriend or older sister turns out it was Shirahai Sempai. What happened? Shirahai confessed to the captain of the Oandan, but the captain turned him down...saying he's not interested in men, so Shirahai came back six month later with some changes and they have been living together since. He is hiding from his family, since his father will kill him if he finds out, he was raised to be the man of men so his family can't find out.

A young girl named Hinomori Asami starts her studies at the Sakura Hill School for Girls in Tokyo, but the capital is a dangerous place, and mysteries abound.
Source: Baka-Updates Manga