Kekkaishi is an anime and manga series centering around 14-year-old Yoshimori Sumimura and his 16-year-old neighbor/childhood friend/"partner" Tokine Yukimura. During the day, they are just ordinary (if slightly sleep-deprived) high school students, while at night they defend their homes and school grounds from monsters (Ayakashi) by conjuring multi-use barriers (Kekkai). They're eventually joined by the half-ayakashi Gen Shishio, and much later by Souji Hiura, a rather odd young man in his own right.The story is not just as simple as that, however, as the protagonists find themselves and their protectorate involved in the devious plots of evil societies and megalomaniacs whose desires reach farther than mere destruction.In America, the anime premiered in May 2010 on [adult swim] (with English dubbing) and on Hulu in early 2011 (in Japanese with English subtitles). The manga concluded in 2011. Yoshimori, Tokine and friends appear in the Massive Multiplayer Crossover game, Sunday VS Magazine Shuuketsu Choujou Daikessen. The anime is currently streaming on Neon Alley.
Accidental Pervert: Yoshimori has one memorable moment in the manga. Luckily for him, he isn't caught. Unluckily for him, he's entirely aware of how bad his blunder is and gives himself no end of grief over it.
Alien Geometries: The Castle of Karasumori. It's MUCH bigger on the inside, among other problems. The Kokuboro castle seems to fit this too, though since it was created by a rather capricious and unpredictable kitsune, it's not surprising.
Bittersweet Ending: The Urukai is reformed under Masamori, Karasumori is permanently sealed away, Shichirou becomes the new head of the Ougi clan, the Sumimura and Yukimura houses are freed of their duties and have overcome their rivalry, and Sousui and Yumeji have been dealt with. However, Yoshimori's mother sealed herself in with Karasumori to keep the seal permanent.
Black and Grey Morality: The leaders on both sides of the main conflict are very nasty. It's just a decision between which flavor of nastiness you prefer. The main cast are pretty much straight-up good guys.
Body Horror: That big guy in the Council of Twelve with a bag over his head? Yeah, there's a pretty good reason for that. He's a man-shaped lump of flesh consisting of himself and four of his brothers fused together.
Mudou gives one to Yoshimori and Masamori in his first appearance. He then builds on it by offering Masamori a Sadistic Choice - save his own life or his brother's - and this works in perfect concert with his previous mind games.
In the manga, Yoshimori collects a bunch of Kouya's hair after his death, and gives it to Masamori for proper burial on the dog's home mountain. Much later on, we learn that Masamori has resurrected Kouya using said hair. Later still, he's even done something similar to Mudou!
It's brief, but it gets mentioned a couple of times that humans have turned into ayakashi in the past. It is implied that Gen's family's less than accommodating martial arts tradition may have effected the existence of his ayakashi side.
Cherry Blossoms: There's a sakura tree on the Karasumori school grounds that blooms sporadically out of season. Ayakashi seem to enjoy it a lot.
Conspicuous CG: For the most part, Kekkaishi is an example of the right way to mix computer graphics and hand-drawn animation. The barriers and Instant Runes are done so well that you could watch the whole series without realizing how they were done. But then you see a car moving and it all goes to hell. Automobile animation is still the kryptonite of CG.
Cool Big Sis: Tokine plays this role to Yoshimori in flashbacks and the beginning of the series proper.
Cool Old Lady: Tokiko isn't incredibly friendly, but barring time outside of flashbacks and the series proper, she's likely taught Yoshimori as much, if not more helpful things about techniques and people than his own granddad.
Declaration of Protection: Yoshimori have sworn to protect Tokine no matter what, and it's his main motivation for getting stronger - he doesn't really care about the whole 'true successor' or 'rival houses' deal. Of course, Tokine is generally quite capable of looking after herself, making it a Type I. His main reason (other than the romantic implications) is that she got hurt protecting him when he screwed up an Ayakashi-hunt as a kid. (Making it a Type VII as well.)
Disproportionate Retribution: The Princess finds a seed in the grapes she was eating. Byaku responds by saying that he will make sure it doesn't happen again. And that whoever prepared the fruit will be thrown into the abyss, never to return.
Expy: The true form of demonic swordsman Kaguro is a really obvious homage to Shishio Makoto, with whom he also shares obsession with drawing out the true power of the protagonist, just to provide himself with an interesting opponent.
Grandfather Sumimura looks incredibly similar to Dr. Wily as well as Heihachi Mishima (albeit an obviously less buff version of the latter).
Extreme Doormat: Byaku, turns out to be this, always acting to fulfill the desires of other people because he cannot figure out his own.
Fertile Feet: Lord Uro cause moss to grow on anything surface he touches and later, to make up for all the food he stole, he sprouts strange plants for all the victims bearing as their fruit the food he took several times over.
Feuding Families: Between the Yukimura and Sumimura clans, over which of them is the "true and legitimate heir" to the guardianship of Karasumori. Yoshimori and Tokine, however, think it's pointless and stupid, have no interest at all in continuing it, and show fondness for each other.
Functional Magic: The Kekkaishis' ability to use barrier magic in very creative ways makes it a ridiculously awesome offensive and defensive technique. It also has practical applications off the battlefield as well, as Yoshimori demonstrates by keeping his grandfather at bay when he's trying to sleep.
Invisible to Normals: In addition to many the many beings naturally invisible to humans without supernatural perception, there's also the kekkai around Karasumori, which prevents outside observers from noticing the real world effects of nightly violent battles.
Masamori hides his heart of gold more than most, but he's the type that dirties himself to keep those he loves above the muck.
Jigsaw Puzzle Plot: The plot of the manga gradually shifts into a vast and complicated power play within the Urakai. Every time a new piece falls into place, more gaps in the overall scheme of things appear.
Limited Wardrobe: Practically all the characters who don't have to interact with the general human population on a daily basis suffer from this. Pretty much the only exceptions seem to be Yoshimori and Tokine, who can occasionally be seen wearing normal clothing in addition to their school and kekkaishi uniforms.
Mundane Utility: Magically conjured barriers for exorcising demons are also handy for holding things in midair, tripping people, and keeping your obnoxious grandfather from bugging you while you're sleeping. Similarly, semi-autonomous magical constructs can be used to make a decoy in order to cut class.
One-Winged Angel: Tons. Most ayakashi transform into bigger, tougher and uglier forms if they manage to stay within Karasumori's bounds long enough. Then there are ayakashi masquerading as humans, who assume their true forms in battle. Madarao enters one of these if his collar is taken off. Inverted with Yoki, who becomes smaller and more compact as he powers up, turning from a Mighty Glacier to a Lightning Bruiser.
Roof Hopping: Bonus points go to using kekkai as hopping platforms.
Sadistic Choice: Tokiko had to foist one onto Yoshimori to prevent him from probably killing everybody in the school in an attempt to save the students from a swarm of (obviously Invisible to Normals) ayakashi butterflies.
Sexy Mentor: A relatively subtle example, but in the last chapter, Yoshimori is clearly trying to invoke this trope when he offers to teach Tokine how to cook when no one else is at his house. Tokine counters by offering to mentor him in math, which terrifies Yoshimori.
Atora is much better example, as she was this to Gen before he died.
Shipper on Deck: Madoka, Tokine's best friend, seems to be fond of the idea of Tokine getting together with Yoshimori as she finds the fact that the two are childhood friends appealing. Kyoko and Ayano support Yurina, a classmate of Yoshimori, since they think she has feelings for Yoshimori after misinterpreting the two's rooftop discussions on spirits as romantic confessions. Yoshimori's father is also apparently a Yoshimori/Tokine shipper.
Ship Tease: Tons between Yoshimori and Tokine. And Byaku and the Princess, of all people.
Shōnen: Yoshimori is 14. He wants to get stronger so he can protect Tokine. And he does.
Standing in the Hall: Yoshimori has to do this in one episode, but cheats by putting the bucket atop an invisible kekkai. Silly kekkaishi, that never works!
Star-Crossed Lovers: While the whole "coming from rival familes" thing fits Yoshimori and Tokine, the trope grand prize goes to Tokimori Hazama's affair with the Princess of Karasumori, who he was hired to protect.
The Stoic: Byaku practically never shows any emotion, even in the heat of an intense battle.
Supernatural Sensitivity: The Sumimura and Yukimura kekkaishi have the ability to sense when an Ayakashi enters the Karasumori site.
Theme Naming: All of the males who were born into the Sumimura family have given names ending with -mori. All of the females born to the Yukimura family have given names that begin with Toki-. Both apparently derived from the founder of the Karasumori Kekkaishi, Hazama Tokimori.
The Thing That Goes Doink: A shishi-odoshi is shown several times at Urakai headquarters and in both the Sumimura and Yukimura family gardens.
Walking Wasteland: Chushinmaru, Lord of Karasumori, wiped out whole towns and forests due to his uncontrollable power to drain life-force. That, as much as his power to strengthen Ayakashi, is why he was sealed.
Weak, but Skilled: Tokine's lack of strength is made up for by her precision, as noted by Tokiko when she tried Masamori's multi-kekkai technique.
We Have Reserves: Masamori is disgusted when the rest of the Urakai leadership show casual, callous disdain about the rank and file. They explicitly state that their men are of no consequence, and that as long as the leadership survives the Urakai will live.
Whack A Monster: Yoshimori and Tokine end up fighting a mole-like Ayakashi in episode 10 of the anime, Yoshimori at one point even trying in vain to smack it with his weapon as it repeatedly pops up out of multiple holes.