Tadakatsu Honda's Dream, Tournament of Champions. It's Tadakatsu's party VS waves of EVERY strong warrior, including Kotaro Fuma, Nene, Sakon Shima, Kojiro Sasaki and Musashi Miyamoto. It's not very difficult, but the crowning moment of awesomeness comes when Hideyoshi and Ieyasu comes to agree he's the Strongest Warrior of Japan.
Nene's Dream, Melee at Sekigahara. Why is it so awesome? It is you, Okuni and Hideaki Kobayakawa vs Eastern Army vs Western Army. And you cut into their battle.
Hideyoshi's Dream: He's faking the dead and surprising everyone in Sekigahara. Admittedly, it quickly becomes unfair when Shimazu and Tachibana defect to the enemy and many officers attacking your main camp at once. But what makes the stage awesome is that Hideaki Kobayakawa, Hiroie Kikkawa, and Hidemoto Mouri stay loyal to Western Army (though Hiroie and Hidemoto is quick to overrun). Hideaki shares heartwarming conversation with Hideyoshi where he's glad that he stays loyal. Mitsunari also shares heartwarming conversation with Hideyoshi where he's happy to know that Hideyoshi is alive. Then, when you approach Masanori and Kiyomasa, Hideyoshi throws What the Hell, Hero? to both of them and brushes their excuse to side with the Tokugawa because their betrayals have thrown the land into the state of chaos again. When Masanori has the audacity to shift the blame on Mitsunari, Hideyoshi simply responds with "Repent, Masanori."
Nagamasa Azai is all about Love and Honor, right? But his whole story shows it is impossible to have both. At least, until... His final chapter, which is a harder version of his first chapter. In it, he decides to deal with his honor to Asakura but cleverly plotting against them, for his Honor and Love belongs to the Oda alliance. So he needs to defeat Nobunaga, only then to turn against Asakura and assist Nobunaga Oda in destroying the Asakura clan.
What's more? The remaining Oda-Tokugawa generals also side with you once this happens. So, it's actually possible for you not to defeat any of them (sans Nobunaga) at all and thus gaining more allies on your side after Oda and Azai join forces. To do this, make sure you have fast horse (Matsukaze is the most recommended), avoid fighting any Oda generals and run straight at Tadakatsu's position (but don't fight him) to enter the forest section where Nobunaga was hiding to reveal his position on the map. Once he appears, immediately run to Nobunaga's position and defeat him as quickly as possible (because at this point, Azai officers may start struggling as they're fighting against Oda officers and it's better if you don't lose them). It's insanely difficult, of course, because you have to avoid defeating them at all and they will wind up on you when you fight Nobunaga. But if you succeed to defeat Nobunaga without losing any Azai officers and defeating Oda officers, it pays off. All Asakura reinforcements will be wiped out quickly and all it's left is the poor Yoshikage.
Gracia's final stage in SW3:XL, Mitsuhide who is widely believed already dead, has come out of his hiding and saves his daughter. Then, inspired by his daughter's bravery and devotion, he raised his own army which includes himself, Gracia and her three friends Kai, Nene, and Mago. Later thanks to Nene, some officers like Masanori Fukushima and HideakiKobayakawa also leave their service from Eastern army and join Akechi's ranks under the order of their "mom". Gracia also reconciled with her stubborn husband TadaokiHosokawa. Finally, both Eastern and Western army are subjugated. The land is united under Akechi banner, both Mitsunari and Ieyasu have resolved in peace and become Mitsuhide's advisers. Yup, it's a Daddy's Girl's Power of Friendship and Love which manages to end the Battle of Sekigahara in a least bloodshed result, considering both of the faction's leaders are still alive and resolved in peace. Said girl's father also become the shogun.
One of the DLC levels in Chronicles 3 is a re-telling of the story of Momotaro and the awesome factor comes from the fact that it has far more regular Mooks than any level in the game, allowing the player to rack up an insane KO count.
The Spirit of Sanada is basically Yukimura's Took a Level in Badass: The Game, especially the final chapters wherein he reaches full maturity. Some notable moments:
Masayuki's duel against Nobunaga, which requires taking his health down four times!
Child Yukimura acting as a bodyguard for his older sister en route to Akuchi, tackling an armed adult who was about to kill Chacha's handmaiden, then fighting alongside Kunoichi and Sasuke during the escape.
Kunoichi and Sasuke beating up all of the ninja that had them surrounded while trying to attack each other.
Sasuke's declaration of, "I am Lord Yukimura's ninja!"
Playing out the entirety of Yukimura's One-Man Army moments from the Osaka Winter and Summer campaigns. Summed up during the final battle with this exchange:
Masamune: Give it up, Yukimura! You're exhausted, wounded, and we have more reinforcements on the way!
Yukimuira: I will never retreat!
Samurai Warriors 4 doesn't allow in the way of Hypotheticals, but Samurai Warriors 4-II had the alternative scenario at Sekigahara where Yukimura, the Tachibanas, Uesugi and Kanegetsu coming in to turn the tide of the battle. Their courage is so noted that several generals from the Western Army thought to have died came Back from the Dead to lend a hand.