Neco-Arc (ネコアルク, Neko-Aruku?) is a Neco Spirit appearing in the Tsukihime series. She is a pint-size cat girl parody of Arcueid Brunestud, acting as the mascot character of Type-Moon at times. In Fate/Grand Carnival, she appears as Mysterious Neco X (謎のネコX, Nazo no Neko X?), parodying Mysterious Heroine X/Artoria Pendragon.
Neco-Arc is a member of the Neco Spirit race, originating from the Great Cat's Village. She became Ms. Ciel's student, constantly acting up in retaliation for having such little screen time and wishing people to think she is smart. She is referred to as the "work of Kischur Zelretch Schweinorg" according to Aoko Aozaki, suggesting she was brought from another world, but it's also said that there is a "certain urban legend" telling of six Neco-Arcs and one that exceeds them that could be a materialization of TATARI.
Neco-Arc is known as the biggest small-fry in the Cat Kingdom. Most characters are unnerved by her appearance, and she especially torments White Len, calling her a "tsundere", and Satsuki Yumizuka, who Neko-Arc constantly reminds that she doesn't have a major role in Tsukihime. She recognizes Miyako Arima as a much-awaited future rival.
Neco-Arc accompanies Ciel-sensei during the "Teach Me, Ciel-sensei!" segments after the player reaches a bad end.
Fate/tiger colosseum Upper
She is a playable character in the Fate/tiger colosseum Upper.
Carnival Phantasm & Fate/Grand Carnival
Neco-Arc (Mysterious Neco X in Grand Carnival) and her fellow Neco Spirits run Ahnenerbe, the strange coffee shop that once every ten years allows worlds to converge. Each episode begins with a short skit of them at Ahnenerbe, which ends with the Neco Spirits turning to the camera and declaring "It's starting!" before the opening credits play.
Melty Blood Back Alley Alliance Nightmare
She also makes appearances in the stop-motion extras at the start of the Kara no Kyoukai movies.
TYPE-MOON has announced two fake films as April Fools' Day jokes. The first was Neco-Arc The Movie, and the second was Neco-Arc Evolution. Evolution was produced by "Twentieth Century Cats" and its theme song was "Neco Illusion 2009." She also appears in Carnival Phantasm where she usually is the one who starts the show-off.
Neco-Arc is the second strongest character in the Nasuverse after Magical Amber. Taiga Fujimura would obviously lose to Neco-Arc. She is twice as strong as Arcueid, but she is weaker than Berserker because cats only have nine lives compared to his twelve.
All of her techniques are extremely powerful like "Dead Neco-ning" and many more, able to destroy everything in her path. Her eye beams are called the "True Ancestor Beam", a "vaguely familiar blast" that cannot be fully observed with the naked eye. She has a warp skill called "Opuba!". Her uppercut, "Cat Out of Hell", sends the opponent flying into the heavens. Her killer move is I want to go to the Crocodile Garden (ワニ園に行きたいわたし, Wani-en ni ikitai watashi?), where she attacks horizontally by turning into a rocket. Like the rest, its fearsome effectiveness is seriously troublesome, and it may have some connection to the Farewell, Ciel-sensei! Our friendship ended in the Crocodile Garden! (さらば知得留！ ワニ園に散った友情?) technique of her third character popularity poll command list. The Elite Neco Corps (エリートネコ部隊, Erītoneko butai?) summons the GCV's only military unit, but while they boast in power, it is unrelated to its power as a technique. The high degree of randomness in that she cannot control them makes it only useful as a provocation.
While originally modeled as a feline, it is hard to tell if Neco-Arc can still be called a cat. She first appears in Tsukihime, where she "assists" Ms. Ciel in giving the player information on how to avoid the bad endings. She later appears briefly in the Tsukihime PLUS-DISC and makes an appearance in a few scenes of Kagetsu Tohya. She was first made a boss character in Melty Blood Re-act, and they gave her many "ridiculous skills." She was later made into a playable character. Arcueid occasionally changes into Neco-Arc in some comedic scenes in Kagetsu Tohya, and some characters refer to the Neco-Arc of Melty Blood as if she were Arcueid herself. She is treated as both a separate entity from Arcueid, and just as a facet of her personality.
There were originally to be Akiha, Len, and Ciel-type Neco-Arcs along with the Arcueid version, and they even recorded lines for them. Though they were "pleasantly strange characters", capacity problems meant only the Yuzuki Ryouka version could be implemented. Nasu would still like to use them if possible.
- Melty Blood Act Cadenza PS2 site
 Melty Blood Act Cadenza PS2 Manual - Dictionary: Great Cat's Village [Place name], p.057
Great Cat's Village [Place name]
The mysterious, unearthly kingdom of cats. Also known as the GCV. An underground kingdom that is both everywhere in this world, and nowhere.
Its size is constantly fluctuating from village to cottage to company, but in the end it's basically a village. There are some that say it is the dream of a certain mighty cat.
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Neco-Arc [Unknown], p.186-187
Ciel-sensei's student. Originally a feline, but it's hard to say if this thing can even be called a cat anymore. In class, she constantly acts up in retaliation for having such little screen time. Details are unknown, but it seems she wants people to think she's smart.
In Melty Blood Re-act, she finally made her debut as a boss character. Of course, we loaded her up with a bunch of ridiculous skills.
With the eye beams, "True Ancestor Beam", the vaguely familiar blast, "Opuba!", the warp skill, "Cat Out of Hell", the uppercut that sends the opponent flying into the heavens, "Dead Neco-ning", and many more, she destroys everything in her path.
Though it seems that she is the biggest small-fry in the Cat Kingdom, to begin with the Cat Kingdom itself is getting smaller every time it appears.
By the way, we actually recorded lines for Arcueid, Akiha, Len, and Ciel-type Neco Arcs. They were all pleasantly strange characters. Unfortunately, due to capacity problems we were only able to implement the Yuzuki Ryouka version. Still, if the chance ever comes around, I'd really like to debut the other Neco Arcs, too.
 Melty Blood Act Cadenza PS2 Manual - Dictionary: The Six Monster Cats, And… [???], p.050
The Six Monster Cats, And… [???]
A certain urban legend tells of the existence of six Neco Arcs. Could this be… another so-called Tatari?
Furthermore, there's also a rumor about a shady being that exceeds even the Neco Arcs. Chaos!
 Melty Blood Act Cadenza PS2 Manual - Dictionary: Arima Miyako [Person's name], p.059
Miyako Arima [Person's name]
The Charging China Girl.
A young girl that (secretly) idolizes Shiki as her big brother. Currently a sixth-grader in elementary school.
After his traffic accident, Tohno Shiki was adopted into the Arima household, and it seems that for Miyako it was love at first sight. However, she had no idea how to deal with suddenly having an older brother out of nowhere, and ended up repeating the same cycle of awkward communication over and over. In the years leading up to his return to the Tohno mansion, she didn't manage to have a proper conversation with him even once.
"This house has a dojo, but nobody ever uses it. What a waste!" Thinking that, Miyako started practicing (self-taught) kempo every day. Though it's merely pretend baji quan at the level of a child's play, in Melty Blood it became the real thing for a single night due to the Tatari's influence. Of course, this delighted her to no end.
Also, she is recognized by Neco Arc as a much-awaited future rival.
 Comptiq 2007-05 issue - Fate Dojo Q & A:
Q: Who's the top three strongest characters?
Q: In Nasu's work (Kara no Kyoukai, Tsukihime, Fate, DDD) Who's the top three strongest characters?
A: Magical Amber, Neco Arc, and Tiger. Well, not really.
Seriously, it's Arcueid, "Ryougi Shiki", and primordial demons.(Not counting Servants)
 Fate/stay night Premium FanBook, p.047 - Q: How strong are Servants?
Q: How strong are Servants?
Nasu: Well you see, attack power is about the same as one fighter. A fighter has way too much power for one person too stand up against, but to destroy one city they'll have to refuel many times. But what makes these guys dangerous is that since they're spiritual bodies, regular weapons won't work against them. As far as destructive power goes, there are more numerous powerful weapons among modern ones, but as normal weapons won't do a thing to them, they're among the most powerful. Anyway, just as fighters can load a nuclear warhead, they each have their own Noble Phantasms and among the Servants there are ones that have ridiculously powerful ones. That's why when I meant strength being the same as a fighter I thought it would be easier to image. Oh and, if I were to say it in a sort of non-serious way, they'd be 1/4th of Tsukihime's Arcueid I suppose? The strength of one I mean. Against one Servant, Arc would probably win, but against two, while Arc's having trouble against the one, the other could get behind her and nail her... maybe.
Q: That's more like, whoah, Arc's tough, heh.
Nasu: (Grinning) 1/2 of Neko Arc.
きのこ：これはですね、攻撃能力はだいたい戦闘機一機分なんですよ。 戦闘機は個人で立ち向かうには強力すぎる力をもっているけれども、 一つの街を滅ぼすには何度も補給しなければならない。 ただ連中（サーヴァント）が厄介なのは、奴ら霊体なので通常攻撃が効かないんですよ。 破壊力においては近代兵器のほうが強力なものが多いんですけど、 通常兵器が聞かないと言う時点でいまだ最強。 で、戦闘機も核弾頭を搭載できたりするように、宝具をそれぞれ備えており、 中にはとんでもない宝具を持ってる奴がいる。 だから、強さは戦闘機ぐらいだと言うのがイメージしやすいかなと。 あと、ギャグっぽく言うならば「月姫」のアルクェイドの4分の1くらいかな？ 一人頭の強さは。サーヴァント一人だとアルクが勝つだろうけど、 サーヴァント二人だとアルクがてこずってる間に後ろからプスッと…いけるかな。
- Neko Arc: "Nine lives! It seems that cats have nine lives so we are a little weaker than berserker."
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: I want to go to the Crocodile Garden [Technique name], p.191
I want to go to the Crocodile Garden [Technique name]
Neco Arc's killer move. J214A. She attacks horizontally by… turning into a rocket!
It seems that there may be some connection to the technique "Farewell, Ciel-sensei! Our friendship ended in the Crocodile Garden!" that appeared in Neco Arc's command list in the third character popularity poll.
Also, this is totally unrelated, but all of Neco Arc's techniques are extremely powerful. Something like the True Ancestor Beam can't be fully observed with the naked eye. Of course, this technique is no exception – its fearsome effectiveness is seriously troublesome.
Incidentally, aren't there crocodiles in the Great Cats Garden…?
 Melty Blood Act Cadenza PS2 Manual - Dictionary: Elite Neco Corps [Technique name], p.059
Elite Cat Troops [Technique name]
The Neco Arcs summoned by Neco Arc. The GCV's only military unit.
It is a self-defense force composed solely of specially chosen Neco Arcs whose overflowing savage nature, excellent physical ability, and unmatched intelligence cannot be controlled. These chosen few are known as Abaddon's Beret, and are the envy of all the Neco Arcs.
Of course, that's completely unrelated to its power as a technique. There is a high degree of randomness involved, so it's really only useful as a provocation.
Probably, this was done in order to faithfully translate the idea that even Neco Arc cannot control the Neco Arcs into game mechanics.
Also, recently there have been rumors swirling about a Dark Chaos Corps, but…?