Signum's fight against Cypha in Chapter 6 of Force was pretty awesome. Wiping the smirk off her face twice in rapid succession with her speed, slamming her into the ground without her arm, and doing it all with the same reserved grace we've come to expect. If not for the Healing Factor and Divider, Cypha would have lost right there.
Nanoha has taken yet anotherlevel in badass and firepower as she goes toe to toe with Thoma and actually has the upper hand.
Newcomer Isis displaying massive skills with explosives. She also disguised her explosive materials as a sewing kit.
Deville's own entry to the fight, where he does a Dynamic Entry on Isis to knock her out in one hit and also nearly manages to get Nanoha In the Back. Without Reacting. If Fate wasn't as fast as she was, things would have turned out differently.
Fate in turn swoops in on Deville, who's already a Lightning Bruiser, so fast he thinks she teleported. There is no ceiling on the badassery of these people.
What makes this even better? She wasn't even in her Sonic Form when she did that either!
Said Diabolus ex Machina also counts as a crowning moment for the Hückebein leader, Curren. To put things into perspective she managed to reach to TWO moving spaceships, snuck her way through Hayate's guard to backstab her and then proceeded to curbstomp said guard composed of Vita and Erio who are already armed with Strike Cannons (weapons designed to fight carriers of the Eclipse Virus; an advantage that Signum lacked). Curren just destroyed the new toys with a simple katana and then disabled both warriors by cutting them with paper. No need to use a Healing Factor and no need to exploit a Story-Breaker Power—she just comes and kicks butt because she's just that good. That screams badass.
Another bit to consider: Hayate packs so much magical power to the point she could still drop her nuclear magic on the Hückebein anyway, who are Anti-Magic incarnate. Even a Reacted Cypha (who maimed Signum prior) was shitting herself since Heimdall Phalanx Shift was too much even for her Dividers to handle.
Subaru pulls an incredible Big Damn Heroes in Chapter 14, where she appears in the nick of time to save a disarmed Nanoha (Thoma just finished ripping apart her AEC Fortress equipment complete with the Strike Cannon) from a lethal attack from Thoma by catching his Divider with her Sword Breaker, damaging its blade in the process and taking it apart with her Revolver Knuckle.
Fate gets a pretty good BDH herself. The Book of the Silver Cross is about to teleport away, wasting the efforts of the battle, and then....
The entirety of the Evil Versus Evil fight in Chapter 19. To be more specific Veyron and Arnage fight against two other EC Drivers to prevent misblaming on the Hückebein family because of their actions. At first seems they're more than a match for the two Hückebein but soon Arnage reveals her Reacted Divider's 2nd form and Veyron just demonstrates why he deserves his spot among the most feared family of killers by turning the tables and annihilating his opponent. He may be have the weaker weapons among the Hückebein family but BOY he knows how to use them!. Veyron displayed such badassitude here that it almost matched Curren.
What makes Veyron more badass is the fact that he DOES NOT have a Reacted Divider and was holding his own against a reacted EC Driver... until he got pissed off and decided to kick the living daylights out of his opponent.
Chapter 24: Instead of the evened out fight people were expecting from Signum and Cypha's rematch, the Blazing General uses her new weapons (as in, the first time she was actually using them in a real battle) to force the latter to run away in the span of one chapter. Makes you wonder what will happen when she gets that Fifth Gen device...
Another one goes to Cypha who managed to fend off an upgraded Signum quite well and was even able to deal major damage despite the AEC Gladiator unit. Hell, she was even able to destroy Signum's needle-shooting shield with her bare fingers! Sonica confirmed in Chapter 25 that Cypha was unnaturally prideful and soft during said fight but ultimately decided to forfeit the match in order to get her job done showing that Cypha, despite being a psychotic smug snake, is a professional who knows when to prioritize work over pleasure and given Signum's condition at the end of the match (half of her unit destroyed and the other half almost ran out of juice), one can say Cypha still had a good chance to continue the fight or even to turn the tables around.
Teana's sharpshooting during the Grendels' arrest: she manages to pop the tires on their speeding truck with pinpoint accuracy while standing on the back of a speeding motorcycle steered by Erio, and then acts like it's totally no big deal. Well, yeah, it wouldn't be a big deal for the Aces like Fate and Nanoha, but Tea is the franchise's poster girl for the Badass Normal trope—no Super Speed, no Super Senses, just an analytical mind honed to perfection and a whole lot of training.note This was before the ViVid anime revealed that Teana has technically been an ace (read: "S-ranked combat mage") herself for at least two years at that point...
To add to this moment, thanks to this, Teana's the first member from the original Riot Force 6 team to successfully apprehend an Eclipse Driver on her own, much less twonote Thoma was ultimately pacified by Lily, and the other two members of the Grendel family were taken out by Cypha and Isis. Not even the Aces could claim that. That said, the reason the Aces didn't make that claim was because they are extremely overpowered—later on, Nanoha pacifies the entire Grendel family (with their Dividers and all) with a single shot, while the news that they are being guarded by Hayate Yagami herself forces them to abandon all plans for escape outright (until she leaves, anyway).
Also, this chapter saw the first deployment of the Oxtongue—essentially a mass-based weapon with some magic-firing capabilities that let it fly under the radar as a "hybrid" model—and despite the Bureau's strict ban on mass-based weaponry, Enforcer Lanster was given an exclusive permit to use it. In other words, out of all their agents, the Bureau trusts Tea to dance on the very edge of the legal system without ever crossing the line (and that after the whole thing with Runessa). Take a wild guess how exemplary her previous record must have been to gain that much trust with the brass.
Chapter 25 gives one to Kurt Grendel. Even though he is seen as an idiot by his family members, they are loyal to him for a reason. He knows damn well that the four of them are rigged with an explosive to kill them if they speak, but is willing to do so if it benefits his family members at the cost of his life. Which is what he exactly does by spilling all information on Hades Vandein and his company to Section 6 anyway. Thankfully, he was saved because the explosive was relocated before he confessed.
Chapter 28: Another Evil Versus Evil fight. Hades Vandein shows us that he is not a Non-Action Big Bad by engaging in a 3-on-1 situation with Curren, Veyron, and Sonica. What makes it more impressive is that not only he is holding his own, but he is the first person to No Sell the Hückebein's attacks. That's right, he pulls a No Sell on two of the most notable members of a family who have been noted for being borderline-invincible.
Chapter 29: Curren is about to make an attack on Subaru, Fate, and Erio only to get intercepted by the latter two by getting shishcabobed by the AEC weapons and promptly electrocuted. Then Subaru promptly smashes Veyron into a wall with her fist followed by Teana who takes charge and fires injection bullets into the three Hückebeins to slow down their healing abilities. Sure, Curren ends up escaping, but it shows how far their AEC equipment is fairing, especially when Veyron points out they now no longer have a one-sided advantage. Yes, one of the Hückebein acknowledged how they are no longer 100% invincible.
And unlike Chapters 13-14, their escape didn't turn out very smoothly. Hades intercepts Veyron and Sonica, shoots out the latter to isolate the former, and comments how their attempt to blind everyone only helped him. But before he could touch Sonica, Veyron intervenes and takes a blow for Sonica at the cost of his heart. While the focus of the Big Bad seems to have shifted in favor of Hades, it's nice to see that the Hückebein are starting to falter.