The final battle with Alma and friends against Kenmi.
The old costume looks better IMO.
Classic example of a human shield.
Summary:
Kenmi powers up after absorbing Unit 0's core and declares that he is going absorb Alma, Ruri, Knight and Fei's powers as well. Knight confronts Kenmi, but Kenmi nabs Fei and flies to the outside. Knight follows but gets beaten up because Kenmi uses Fei as a human shield. Back inside Kenmi's compound, Alma tells Ruri to help him transform, and Ruri states that Alma has the power inside and doesn't need a gem to transform anymore. Alma transforms into a new form and goes off to help Knight. Back on top of the compound, Fei tells Kenmi to kill her so Knight can fight without holding back. Kenmi obliges and tries to crush Fei's neck and Knight is too beat up to stop him, but Alma cuts arrives and severs Kenmi's arm and frees Fei. Kenmi however absorbs Knight's energy and starts fighting Alma, and Knight ends up falling back down into the compound. Kenmi tries to absorb Alma, but Alma tosses Kenmi into Mount Fuji and the fight moves to mountain. After seeing Knight fall through the roof, Fei becomes distraught and transforms into an Ashi Mickey Mouse.
It's Ashi Mickey Mouse!!!

24 karat gold plated everywhere baby! Nobody is more bling than me!!
Back inside Kenmi's compound, the maids have located Ruri and are escorting her. Meanwhile, Aoi wakes up and finds Onigawara in her room. Elsewhere, Kagami shakes off Arakune and goes to find Aoi, and Arakune isn't too interested in giving chase. Kagami's job is made much easier thanks to Onigawara's arrow projections, and Kagami gathers Aoi and Onigawara to meet up with Ruri's group. At Mount Fuji, Alma beats on Kenmi but Kenmi is unfazed. Fei arrives and peppers Kenmi with projectiles, but instead of hurting Kenmi the projectiles actually give Kenmi a coat of armor that renders most of Alma's attacks useless. Fei leaves after realizing that she is not helping the situation and when she hears Knight's voice begging her not to fight. Kenmi thinks he has the fight in the bag and starts spewing secrets (such as how he had Unit 0 kill Ruri's parents), but Alma picks up speed by running a few laps around Mount Fuji and then blasts Kenmi with a super drill punch that sends Kenmi flying back onto the roof of his compound.
I'm gonna drill punch you back to the Stone Age your house!!!
Hovering Pyramid of Doom.
Fei and her Knight in shining armor.
Kenmi is mortally wounded by Alma's attack, but Fei happens to be nearby. Kenmi grabs Fei and falls down the hole in the roof, and during the fall Kenmi gives Fei his core so Fei will absorb the hate and go nuts. Kenmi dies after the fall. Fei loses her Ashi form, but she encases herself in a giant upside down triangular pyramid which rise into the sky and starts shooting out beams everywhere. Inside the compound, Knight wants to save Fei but he doesn't have the energy to transform, but Aoi arrives and uses the gem on her necklace to help Knight transform into a Sacred Seven form. Knight flies out to meet up with Alma to work out a plan. Alma uses his powers to seal the pyramid and prevent it from falling, while Knight uses his "walk through walls" power to get into the pyramid and extract the rotten core from Fei's body. Fei is saved and flies off with Knight. Alma returns to the compound where Ruri and Aoi share an emotional embrace.
Aoi: I sleep for a couple years, and now I'm the little sister?
In the days after the battle, Ruri and the Aiba Foundation set things right again, and all the maid are hired back. Knight and Fei are looking cool on a tower somewhere. At a cemetery, Arakune visits Kenmi's gravestone and leaves. At the end, Alma, Wakana, Nanami and Ageha join Ruri, Kagami and Aoi on a leisurely cruise on Ruri's boat.
The appearance of peace is merely a temporary illusion...
And I thought Ruri would have a bigger boat than this.
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It wasn't exactly a great finale, but I guess we shouldn't expect too much given the show itself and how the build up to the final showdown only started in the previous episode. As expected, Kenmi goes bat-shit crazy and starts screaming nonsense, and despite Fei helping him on every turn Alma still kicked his ass single-handedly. The battle against Kenmi was alright, but we've seen better from this series. Alma's lapping drill punch was kind of cool, but I was disappointed that Arakune was just written out of the battle instead of doing anything significant. Fei was still the most disappointing of all though. She just completely sucked this episode. At the end of the previous episode it looked like Fei was going give Kenmi a personal ass-whooping, but instead Fei ends up helping Kenmi in the battle over and over again: first Kenmi uses Fei as a human shield against Knight, then Fei gives Kenmi an armor power up (not really sure how that worked), and then Fei herself turns into the final threat. Fei should have just hid in a corner or something. The whole final segment with Fei turning into the Hovering Pyramid of Death just seemed unnecessary given we've got Kenmi the batshit crazy villain. Just give Kenmi some more improbable power ups, and then have Alma and new Knight work together to put him away. Sometimes going with the predictable route can be a good thing.
Overall, Sacred Seven was certainly not a good series especially when plot or even pacing is concerned, but at least it wasn't boring. The over-the-top action is mostly decent and can be pretty impressive at parts; the production quality is very good just as what one would expect from Sunrise, and the comedic parts can be somewhat amusing. I just wished the show would have spent a little bit more time building up to the final showdown with Kenmi though. Sacred Seven is not a series to watch for enlightenment, but it's not a bad way to kill a couple hours of time. Supposedly a special/OVA focused on Knight would be made, so the people who enjoyed this series will have something more to look forward to.