Original series (Vol 1-9). Ran for 100 issues. 1987 to November, 2002 (Yes, fifteen years). The first bulk is mostly that of Jeremy's adventures with a few stories focused on side characters. Later on most of the stories focused on Ricky and his own entourage of girls (In this case Lendo's step-sister Yumei, Superhero Heidi, and a Salusian Princess with a purchased title, Solora). This is considered Vol 2 of the series. There is also the mini series "Quagmire USA".
Hawaiian series (#101-129, December, 2002 - June, 2005): Focuses on supporting character, Yumei, as she goes to Hawaii under the request of a family member and has her own adventures.
Shidoshi series (#130-175, August, 2005-August, 2009) : Continuation of vol 2, something of a reboot of the series to distinguish it from the original. The story now focuses entirely on Ricky and a new cast of characters as they come into conflict with a deadly rival ninja clan.
Revival series: (#176-Current, June 2014-Present): The third volume of the series. A new alien race calling themselves the "Kuroni" have possessed the people of Quagmire and plan to enslave all of Earth. Anne Feeple and Prof Steamhead are the only two unaffected and are forced to jump to an alternate dimension to find means to defeat them. Thus setting this series in a new world.
Animesque: Dunn is an admitted anime and manga addict. In fact he's know as the "Grandfather of American Manga" due to being one of the earliest artists to use the style in U.S long before manga became a normal commodity outside Japan.
Art Evolution: Not surprising since the series started in 1987. The first artwork was mostly that of a usual American comic book. Then evolved into more manga like standards, likely Ben experimenting with his art and sticking with the latter style.
Beast Man: Salusians' natural form, which resembles a bipedal skunk. When humans are transformed into this form, they, much like Salusians, retain one marker of their species - in this case, a lack of a tail.
In fact this becomes a major theme in the second half of the series and fuels the conflict with the Elder Stars who are so rooted in their traditions that the protagonists are forced to go against them if they wish to run their own lives. In fact it was because of this that the rival ninja clan, Shidoshi, were created in the first place.
Betty and Veronica: Asrial to Betty and Ichi to Veronica. I mean they even got the same hair color!
Big Bad: The Shidoshi during the Ricky era of the series.
Bittersweet Ending: The Hawaiian and Shidoshi arcs For the former, Tetsuo, being the brat he is, tricks Yumei into marrying a Ricky-bot rather then her true love dispite doing all she can defeat him and it's legally binding so she can't get out of it unless he gives the say so (though later in Shidoshi, after Tetsuo undergoes major Character Development, he gives her the remote to self-destruct the bot and annul the marriage). For the latter, Yuudai dies without having his final battle with Ricky, getting the last laugh in their rivalry as well as a century long revenge against the Red Ninja (though if this is good or bad considering his back story is up to you). Ricky's group take on the Elder Stars and have to settle for just bankrupting them then defeating them in combat. Tetsuo can't marry his true love, Nanashi, but for the time being everything's worked out in the end.
Bleached Underpants: Dunn also wrote a satirical adult series entitled NOT Ninja High School, at the same time as the original. (Other writers and artists have continued releasing sequels.)
Blood Knight: Many characters in the series. Destructo in the original series, and more recently, Yuudai.
Boisterous Bruiser: Arnie the 7 foot tall gun-toting jock, who also shows elements of being a Genius Bruiser with his weapon-building expertise and debates with Professor Steamhead on science matters.
Captain Ersatz: Oh so many, is it any wonder this and Gold Digger get along so well?
One description of the artist's works, and characters. If it's in Ninja High School, it's Ben Dunn.
Cat Girl: Has a few, the most notable being Meppy, a Drill Sergeant Nasty -like gym and health teacher, who fought Nazis during World War II.
Defrosting Ice Queen: Ichi initially as she only wanted marry Jeremy to become leader of her ninja clan. But the more she comes to know Jeremy the more she seem genuinely willing to marry him. Ultimately it doesn't happen and she marries Lendo.
Disappeared Dad: Jermey's, subverted as he finds out his dad is Trapped in Another World, a mouse based one, highly ironic in that Mr.Feeple's profession is a rat exterminator. What's more, he is now the king of the land and can't return to the human one as the mouse people don't have the technology to do so without fatal side effects.
Disproportionate Retribution: Yuudai was a huge victim of this thanks to the Elder Stars' displeasure at the growing closeness between him and Empress Meisho.
Happily Adopted: Anna Feeple (previously Anna Ichinohei), who was brought into the Ichinohei clan after her mother was killed while helping Kudasai during the second World War. In fact, one of the conditions that Kudasai (her adopted father) put on granting permission for her to marry Bob Feeple was that their first-born son would marry the first-born daughter of Kudasai's biological son, so that Anna could finally have a blood relation to the Kudasai clan.
Herr Doktor: Doctors Steamhead and Hossenfeffer. Later justified as a flashback shows both in pre-World War II Germany, as the Nazis were rising in power (Hossenfeffer joined the Nazis; Steamheim, as he was known then, tried to remain apolitical but was encouraged to leave, later joining the Allies).
I Choose to Stay: Anna when she is finally reunited with her husband in the mouse world. One can't blame her considering how long they've been apart.
I Know You Are In There Somewhere Fight: When Jeremy is first brainwashed by Lendo in issue 3, Ichi uses a ninja spell to break into his subconscious and undo the mind control. Also appears later in the Copier issue.
"Please. You're not this person. You're not this person."
Love Hurts: In Steamhead's origin - he was engaged to be married in Germany as the Nazis rose to power. However, he was denounced as being Jewish (due to a grandparent), and his fiancee publicly repudiated him, saying that "Love is no longer possible." Receives a Meaningful Echo later, when she privately tells him that she'll elope with him to another country, but he repeats the line to her and commits to leaving Germany alone... while hiding his tears and committing his life to science.
McNinja: Anna Feeple and both of her sons, although Jeremy doesn't show it off nearly as much. Justified when Jeremy reads Kudasai's diary - Anna was adopted into the Ichinohei clan after her mother was killed trying to help Kudasai during World War II. She remains part of the clan and has taught both of her sons some skills, although Ricky takes to it more readily.
Missing Mom: Yumei Katana's during the Hawaii series We later find out she had went into hiding to get away from her abusive husband (helped out by Anna) and tricked Yumei into coming down to Hawaii so she can look after her. She also married to the above mentioned janitor of the series.
Replacement Flat Character: Lendo became this post Timeskip, after spending most of the series as the antagonistic Jerkass. His role was then filled by a new Jerkass, his younger brother, Tetsuo. Who is, post-second-Timeskip, turning into a Badass NormalNiles himself. Looks like it runs in the family.
Unfortunately, for Tetsuo, at least, it didn't take.
Actually... We find out later this was a ploy to save his girlfriend, Nanashi from the Elder Stars. When he learned that his grandfather, head of the Elder Stars, would have Nanashi killed if Tetsuo did not comply with the arranged marriage to a Chinese Amazon princess his family had set up for him, he chose to go along with his family's wishes to save Nanashi's life. To atone for this betrayal, he sets up a multi-million dollar account for Nanashi, unbeknownst to her..
Royal Blood: "A human is no match for a Salusian of Imperial Birth!"
Royal Brat: Asrial and her sister Andromeda, though not all that bad they have an annoying habit of letting everyone know it when they get the chance.
Royal Rapier: Jeremy is rather adept at fencing weapons, even surprising his friends in Chapter 3 when (while under Mind Control) he was dangerous with a saber. Expanded when he stayed in Japan with Kudasai for a few weeks; as his father was a fan of movies with a bunch of Flynning, he taught Jeremy how to fence. Kudasai seemed rather impressed.
Samus is a Girl: Introduction of Sammi, who was forced to cross-dress due to her father not wanting to lose a bet and go into bankruptcy.
Shared Universe: NHS is loosely in the same continuity as Fred Perry's Gold Digger, with several crossover arcs and miniseries between the two.
Shout-Out: Plenty, in fact the comic pretty much runs on this. In the picture above, Asrial is pretty much wearing the Gundam Double Zeta
The Slacker: Generally, any reference to Ichi-kun's father will be in how he wastes his family's skills on petty parlor tricks (one background image was him using his ninja skills to balance a horde of chopsticks and toys to entertain friends). All indications are that he either passed on the chance to be in line for clan leadership or was simply content to let his daughters contend for it instead.
Sleep Mode Size: Ordinarily, Kudasai Ichinohei (Ichi-kun's grandfather) is a fairly small, if fit, gentleman. However, when Ichi-kun challenges him at the beginning of the comic for leadership of the clan, he dramatically increases in size and takes on a Heroic Build. Later given a Take That in a flashback issue, when Ichi-kun imagines the form with a "Body By Liefeld" sign.
Ricky: That gotta be the second biggest Hitler robot I've ever seen!
Super Strength: One of the powers of a "Salusian of Imperial birth" like Asrial.
Superpowered Evil Side: Cute Witch Mimi has one which nearly took over Hell. Suzume (one of Ricky's ninja partners) also has one that can't tell friend from foe due to her clan's very brutal training from birth.
Take a Third Option: How Tetsuo manages to get one over on the Elder Stars After they deny him the choice of marrying his true love. He decides to play it their way and follow tradition, which means he could spread his secrets to other ninja clans and bankrupt them financially without breaking from their iron clad traditions. Say the least while he doesn't beat them psychically (he tried but was no match) he manages to do so by sheer wit and turning their customs back at them.
Testosterone Poisoning: Akaru, an island native who doesn't know anything about modern civilization and largely judges everything on how manly it is.
Time Skip: Starting with Issue 75, which picks up 5 years after the original series, and later in Issue 168, which takes place seven years after that.
Timey-Wimey Ball: Mita Celande has a time machine, and some of her temporal doings (such as taking Mimi Masters and Jeremy back to when the Feeple line was cursed by Mimi's ancestor) start throwing monkey wrenches in how things are to play out. She eventually has to leave due to a Temporal Paradox (namely, that her ancestors Jeremy and Ichi-kun were no longer going to have children together) potentially negating her existence.
What Happened to the Mouse?: A literal example of this occurs in Issue #14, when a (normal sized) talking rat appears before Jeremy with a message from his father, Bob Feeple inviting Jeremy to Dimension X, where Bob has become Emperor of the Rats. The rat uses a dimensional beam gun to spirit Jeremy, Asrial, and Ichi to Dimension X which is populated by human sized anthropomorphic rats. The original rat is never seen or mentioned again.
What Kind of Lame Power Is Heart, Anyway?: This is actually Jeremy's shining trait in the first series. Despite being surround by supernaturals and extraterrestrials, he can calm a situation simply by being himself and attempting to talk it down. Course if need be he will fight if he has to but the former is his true "power".