Skelter+Heaven

Tenkuu Danzai Skelter+Heaven is an anime OVA produced by Idea Factory and directed by Yoshiteru Satou of Mars of Destruction infamy. It is an adaptation of a visual novel of the same name. Like Mars of Destruction, it is considered one of the worst anime in existence.

Plot
In the distant future, a mysterious floating object appears suddenly in the center of the city from the form of a giant yellow alien squid. The top secret mission unit "Alta Mira Agency" or AA is comissioned by the Defense Agency to deal with this mysterious invader. In charge of the robot training is Hunagai Otsuya. He must choose one of the girls to receive special training which she will recieve in secret. They must use the "Battle Soles" to push back the enemy even at the cost of their lives.

Why It’s Not Heavenly

 * 1) It was created by Idea Factory, the same creators of the infamous Mars of Destruction making it their bastard love child.
 * 2) Much like that said series, it feels more like an extended version of the video game it is based on than an actual spin-off/anime adaptation of said game.
 * 3) The animation and the CGI is outright horrendous and plus the CGI used for the alien squid is so bad that it makes the Berserk (2016) animation look like a masterpiece by comparison! Bare in mind, this came out 2 years after The Voice of a Distant Star, which looks better than this and was made by one person.
 * 4) Dull and bland characters (including the male protagonist, Hunagai Otsuya) have no personality at all and are pretty much forgettable and most of them are very annoying. They also try to have the characters act hammy in order to make them stand out more, but not only dies out but it come of as obnoxious instead, but it doesn't even do anything to save how poorly written and one-dimensional they really are.
 * 5) Despite the anime doing everything in it's power to convince the audience that the yellow alien squid is a monster that must be stopped in order to save humanity, it never actually did anything to harm anyone and was simply floating above the city. And it only started fighting back when the anime's so-called "heroes" started attacking it.
 * 6) Overuse of fan-service even so more then Gantz at least that show they tried to tone it down and there were far less of it during the second half of that seasonǃ As there is a constant usage of pointless shower sequences or exercise scenes involving the girls.
 * 7) Crappy voice-acting and dialogue in which some of the characters have obnoxious screams with the protagonists Hunagai Otsuya and Rin Ichikawa being the worst offenders.
 * 8) *Speaking of the voice acting, it isn't just bad, but also wastes the talents of many talented actors. Like Shizuka Itou (who also voices Yayoi Kunizuka from Psycho-Pass, Akeno Himejima from High School DxD, Sailor Venus from Sailor Moon Crystal, Flare Corona from Fairy Tail, Kyōko Fujibayashi Mahōka Kōkō no Rettōsei, Wilhelmina Carmel from Shakugan no Shana, Misa Kakizaki from Negima! Magister Negi Magi, and Hinagiku Katsura from Gotoku no Hayate), Kaori Nazuka (who also voices Kiyoko Shimizu from Haikyuu!!, Toru Hagakure/Mt. Lady from My Hero Academia, Jenny Realight from Fairy Tail, Miyu Edefelt from Fate/kaleid liner PRISMA☆ILLYA, Yui Kotegawa from To LOVE-Ru, and Tsubaki Nakatsukasa from Soul Eater/Soul Eater NOT!), and Hideyuki Tanaka (who also voices Leo Aiolia from Saint Seiya, Yaozo Shima from Blue Exorcist, and Fujitaka Kinomoto from Cardcaptor Sakura: Clear Card)
 * 9) Most of the fight scenes are boring to watch. As not only are they incredibly repetitive and dull, but they don't feature much actual action (so much so that it's hard to even call them action sequences) like it rely on shooting tentacles of the yellow squid alien.
 * 10) The tone is inconsistent if it's either trying to have a dark tone for that matter.
 * 11) Plenty of nonsensical moments like Misaki and Midori pumping a pumping chair machine.
 * 12) The anime feels the constant need to just randomly throw plot points in without any sort of build-up to them. For example, the battle between them and the giant yellow squid creature has actually cut out twice to show that the girls are actually artificial beings completely out of nowhere. It also isn't helped by the fact that this ends up going absolutely nowhere and gets no real focus or explanation to it.
 * 13) The plot for the anime is boring, stupid, and laughable as a generic "alien invasion" and a "girl-mecha" story.
 * 14) The ending is overwhelming and horrible (where the female protagonist, Rin Ichikawa persumably sacrificing herself to destroy to giant yellow squid ) as it leaves it on a cliffhanger. As it cuts to a year later, with a similar news report as the one that started the anime off, only now, there's multiple giant squid beings about to invade the Earth. And that's where it ends! There's no resolution or anything! it just ends there!
 * 15) Pretty much, this anime is forgettable overall. Again, in a similar vein to Mars of Destruction, it does absolutely nothing new with any of the genres it uses (e.g., alien invasion, action, mecha, sci-fi) and simply tries so hard to be like every other anime with said genres. Which not just causes the series to have no identity of it's own, but it also doesn't even try to be it's own anime due to it wanting to simply cash in on the success of said other superior animes.

Redeeming Qualities

 * 1) The character designs and the mech designs are decent despite being too basic (like Hunagai's skin color being tan and his hairstyle that kinda resembles Shobu Kirifuda from Duel Masters).
 * 2) The opening theme song is pretty catchy.
 * 3) Some decent emotional moments like Rin and Hunagai's relationship despite it was not paced well
 * 4) It has many unintentional hilarious moments due to how bad it is.

Reception
Skelter+Heaven was universally panned by critics and anime fans due to it's poor animation, one dimensional characters, and all the the flaws it has. Due to it's overwhelmingly negative reception, it, along with Mars of Destruction, are widely considered to be some of the worse animes of all time to this day. It currently holds a 1.1% on IMDb.