Keita survived having his terra drained, by Nanase, in order to get to Kuro. When Nanase catches up to to him, she smashes his skull with a rock, and drains what little terra he had left, while giving him a Motive Rant. Keita uses what little strength he has left to wrap his legs around her neck and slam her into the rocks, knocking her unconscious, so he can finally sync with Kuro, against Hiyou. Keita's desire to protect Kuro deepened their bond to such an extent that they both gained dual crests!
Died Happy: At the end of the anime, having lived the rich full life Kuro wanted for him. As a show of gratitude, he takes the curse of the Doppeliner System with him.
Heroic RROD: Keita collapses twice, at different points, due to the excessive strain syncing puts on him, because he's a Sub. Which is part of the reason Kuro leaves him in the end.
Your Days Are Numbered: Had he continued to synchronize with Kuro for much longer, the strain would have eventually killed him.
Big Eater: Which isn't helped by the fact Punipuni often swipes whatever food she manages to get ahold of.
Boxing Battler: She is often frowned upon for using boxing, a human fighting style, when she fights. Doesn't stop her from usually winning. This is changed in the anime to her being more of a Bare-Fisted Monk.
Foot Focus: Which is why you can expect to see plenty of closeups of them.
Genki Girl: With all the crap she has to put with, you'll wonder how she does it. At least, until Keita tells her that she doesn't have to hide her pain anymore, and says it's okay for her to cry. Then the dam breaks.
I Want My Beloved to Be Happy: She comes to realize that the Doppleliner System would remain in effect, as long as she and Keita are bonded to each other. In the end, she parts ways with him and returns to The Pure Place, where she remains 'til the end of her days.
Clingy Jealous Girl: Akane gets the wrong idea when Kuro tries to sleep in the same bed as Keita, to deepen their synchronization, and stays overnight to keep anything from happening. She has another bout of jealousy after seeing Excel kiss Keita.
Cute Clumsy Girl: Her blouse gets caught on her locker, in the first episode, which exposes her cleavage. Also see the Running Gag entry below.
Face-Heel Turn: Subverted. It initially appears this way when Keita and Kuro learn sshe's become Reishin's Contractee. It's eventually revealed she was trying to help Reishin to rid the world of the Masagami and the Doppeliner System.
Feminine Women Can Cook: She takes it upin herself to prepare meals for Keita ever since his mom died, and because she has feelings for him.
Friend to All Living Things: Including Yuki, when Daichi tries to kill her; despite the fact Yuki had threatened to kill Akane with the very same gun, only moments prior.
Messianic Archetype: She takes in Kuro and feeds her, after finding her passed out near Keita's apartment. And as seen above, she even shielded Yuki to keep Daichi from killing her. Akane even goes so far as to become Reishin's Contractee in order to help rid the world of the Masagami and the Doppeliner System.
They dress similarly, so are their mannerisms, both are pale skinned blondes, they're both nobility, both are Older than They Look despite their childlike appearances, both are well informed about the innerworkings taking place behind the scenes of their respective canons, and both take an interest in their respective protagonists.
The pattern of Excel's Hexa Wall even resembles the menu screens from BlazBlue!
One-Man Army: A quite literal example, as Steiner's "Stampede" ability allows him to move fast enough to create an army of speed clones that can attack autonomously. Including individually, in groups, or all at once!
Undying Loyalty: To Excel. So much that he had one of his Stampede Copies carry her to safety, right before he died.
Weak, but Skilled: Yakumo isn't as strong as most other Tera Guardians, but is so proficient in martial arts, that he rarely needs his to use his Exceed. In fact, he's only forced to use it three times!
Well, Excuse Me, Princess!: Double subverted, since Kuro never complains about him, and he realizes Riona's griping stems from concern about his well being.
Big Eater: Moreso than Kuro, much to Riona's chagrin. As shown in the manga, she'll even take time to snack while fighting 40+ Tribal Ends.
Big Sister Mentor: In the manga, Nam becomes this for Kuro and Keita. At first, she kept her distance unless directly threatened, but when she learned of Kuro's circumstances, among other things, she began to play a more active role in the group dynamics.
BFS: She uses a type of Korean sword that also functions as her 'Thousand'.
Boobs of Steel: Hers are even bigger than Akane's and Mikami's. She's also an order of magnitude more powerful than Kuro and Keita (and many other Tera Guardians/Contractors) synchronized. Nearly everyone who's taken her on has been handed their asses by her, collectively or otherwise.
Clap Your Hands If You Believe: Manga only. The reason she came to Japan in the first place was to get onto a TV show so she could enough money to rebuild and fund a temple to her own country's Shinryon (Tera Guardians).
Our Tera Guardians Are Better: In the manga, she is similar to the Motosumitama in that they both considered Terra Guardians but Nam doesn't need to form a Contract with a human and is actually considered a minor deity in her own right with enough power to perform exorcisms.
Pretty Freeloader: From Riona's point of view, since all Nam does is follow them around and mooch off of her. Yet, Nam never wants to help out, 'cuz she's a scribe. She protects Riona several times, during the battle with the Masagami, but she runs off with her snacks at the end! She acts like this at first in the manga but she actually pulls her own weight and even helps to train Kuro and Keita in how to properly synchronize.
See Ya Around, and Yoink!: She pulls this on Riona, at the end, by swiping her bag of snacks, as payment for services rendered, and runs off with it!
Big Brother Instinct: Anime version - You have to give respect to a guy who's willing to slaughter members of his own tribe and family to save his little sister from being executed on her birthday. And knock the natural balance of the entire planet off kilter just for the chance to kill the dark god partially reincarnated as his sister in order to save her (and all life as we know it). Additional awesomeness being voiced by both Katsuyuki Konishi in Japanese AND Crispin Freeman in English.
Hero Killer: Reishin kills Steiner, Bernhart, and dozens of others, mops the floor with Kuro twice, and easily repels/survives even the strongest Exceed abilities. The only ones to actually make him work for a win were Steiner, Kuro (during their final battle), and the Masagami.
Not What It Looks Like: It is actually the elders who killed the innocent people trying to protect Kuro, not him. Yakumo only saw the aftermath that made it looked like he killed everyone.
No Kill Like Overkill: Reishin's Exceed: Tera Cannon. Picture a ring of glowing orbs surrounding the target, then all of them going off simultaneously in the form of massive ki blasts that solidify as they impale the victim from every angle, in a 360║ radius.
Gadgeteer Genius: Daichi manufactures replica Thousands for his followers to use, which generate force shields.
Jerkass: Smug, snide, condescending, self-important... you name it. It's no wonder he didn't have any friends, not that he was trying to make any.
I Shall Taunt You: Daichi loves talking down to those he feels are beneath him, and those he's betrayed. He even ridicules Hiyou and Reishin to their faces... once they're powerless, of course. Then has Raiga kill the former, and arranged to have the latter banished through a wormhole.
Smug Snake: Talks plenty of sh*t, when he takes advantage of Hiyou, who was left weakened from his battle with Kuro. And does the same to Reishin, by waiting 'til he's too exhausted from having fought Steiner to defend himself. Which is when he has Raiga impale him, to use Reishin's tera to empower his followers, all while taunting him.
What Measure is a Sub?: For all his talks about peace and equality for Roots and Subs, Daichi doesn't give two sh*ts about Subs. Once he gets Reishin out of his way, he mocks Yuki for being a Sub, in one of the cruelest "reason you suck" speeches ever.
Klingon Promotion: First he gets rid of Hiyou, then does the same to Reishin, so he can marry into the Kaionji Family and become it's new CEO.
Murder the Hypotenuse: Once Yuki learns that Daichi's been harboring Akane in the penthouse suite of the Kaionji Building, she confronts Akane with the intent to kill her, even if it meant becoming a Negative Root. But she couldn't go through with it.
The Unfavorite: She's the only one of her father's children to not be Master Root. She's a Sub. Three guesses what they think of her.
Unwitting Pawn: To Daichi, who she thought was helping her. Instead, he was planning to kill her once he found her other Sub, and Akane, who's their Main Root. Which would have made Akane a Master Root. So he thought.
Last of His Kind: At first, he shares this spot with Kakuma and Makana, until he sacrifices Kakuma, in order to break the seal on The Pure Place. After he's killed, by Kuro, Makana is left as the last surviving member of the Hima Clan.
Revenge: Raiga wants avenge the Hima Clan of Tera Guardians, who were nearly wiped out under Reishin's orders.
Silent Bob: Until he's face-to-face with Reishin, that is. Then he tells him exactly what he thinks of him.
Bitch in Sheep's Clothing: When she first approaches Keita, she pretends to sympathetize with him over the loss of his mother. She drops the act once he lets his guard down, and steals his tera, so he couldn't help Kuro.
Evil Twin: Nanase was one of his mother's Subs, until she killed the other two to change her fate.
Hot Consort: A flashback reveals she's slept with Hiyou though, judging from her sullen expression, it seems she did it reluctantly.
Screw Destiny: After learning she was a Sub and doomed to a short and unhappy life, she defied the Doppeliner System by killing her Root — Keita's mother — and her other Sub, thus becoming a Negative Root.
Tears of Remorse: Not for the things she'd done, but because she had never known what it was like to feel happiness before dying.
Woobie, Devourer of Souls: Since she's a Negative Root, she has to sustain her existence by siphoning the tera of others. But it doesn't bring her the fulfillment she desires. Instead, it only adds to her misery.
Jerkass: See just about any of the related entires in his section.
Karmic Death: Daichi finds him weakened after he was defeated, by Kuro, and takes advantage of the situation by placing Hiyou in the very device he used to kill countless other Tera Guardians. Then has Raiga do the honors.
Making a Splash: His Exceed allows him to manipulate water by firing needle-like projectiles of it at his opponent. Or, he can turn it into shards of ice. And what's really scary is, he can also use it to manipulate the water in his victim's blood, though it requires him to make physical contact with their bodies.
Shoot the Messenger: He vents his frustration at having lost to Kuro and Keita, by killing one of his Tribal Ends when they tried to relay a message from Daichi. Hiyou didn't even care what the message was about.