For years, paranoid Satou Tatsuhiro has shut himself away in his apartment for days on end, with barely any social contact whatsoever. Then one day when he answers the door, he is greeted by an older woman and a girl called Misaki, who are going from door-to-door to inform people of the recent social problems of hikikomoris. In a fit of depression about his way of living, Satou decides that the only way to escape his current life cycle is to muster up his courage, face his fears, and go outside to find a job. However, instead of employment, he finds Misaki waiting for him; she intends to make Satou her ‘project' so that he can reconnect with society. Now with the help of his friend Yamazaki and Misaki's evening meetings, will Satou be able to escape his hikikomori lifestyle, or will he simply fall deeper into the clutches of conspiracy and his own demons?
Daisuke is popular with all of the ladies at school, including his childhood friend Yuzu and flirty Kazuki. However, there's one girl who not only doesn't like Daisuke, but also seems to be afraid of him – timid, guarded Hinako Aikawa. After proclaiming that she's the only girl he has no interest in, Daisuke accidentally discovers the truth about Hinako and the terrible, horrifying secret that she hasn't told a soul. Though she isn't aware that he knows, Daisuke makes a decision then and there to protect her, slowly realizing that the girl he had no interest in, is suddenly the most important thing to him...
Looking for something that treats very heavy themes where most manga shy away from? Then both Welcome to the NHK! and Bitter Virgin fit the bill. The atmosphere in both is quite similar, even though NHK has some awkward and effective comedy, where Virgin has more angst and romance. If you want to experience that uneasy chest-feeling one of these gave off again, give the other a shot.
Another seinen manga about a huge loser/hikikomori trying (extremely unsuccessfully) to crawl out of the pit he's dug himself into and become cool/popular/normal, with the help of some women who are far from perfect themselves. Both are extremely cynical and a bit depressing, but offset this with tons of black comedy.
Every day after school, the quiet and introverted student Kurosawa goes into the empty girls bathroom and "relieves himself". Besides this extremely odd ritual, Kurosawa also has a thirst for justice and a judgmental attitude towards his classmates. Upon seeing the bullying of an awkward girl in his class by two of the "popular" girls, he decides to bring justice to the bullies the only way he knows how. His plan for revenge goes "just as planned" until met by an unsuspected accomplice.
Both contain a similiar comedic tone (With N.H.K possibly edging more on the comedic side) with damaged and confused characters. Both series also contain a very similiar message and the same descent into dark territory. If you like one; you should definately try the other.
Another seinen manga about otaku/hikikomori with a similarly cynical approach. Both are pretty bleak, but while Welcome to the NHK! covers a huge array of awful things that can happen, Ressentiment is more focused- people who liked the eroge and MMORPG story arcs in the beginning of NHK! the best are the most likely to also enjoy Ressentiment.