Battle Harem

A subtrope of the Harem Anime genre, where the male lead has a harem of potential love interests, all of whom are some sort of Action Girl. Sometimes the harem may appear in a form of Hero Secret Service or as an Amazon Brigade.

Because this is a more action-oriented subgenre, Battle Harems are less likely to be focused on romance, but still provide plenty of Fan Service. Often this appears in the form of a Supporting Harem.

Related to Harem Hero.

Anime and Manga

Mahou Sensei Negima has over 20 women, most of whom are Action Girls in some form or the other, and most of the rest being at least Plucky Girls or otherwise quite useful in some way.
Mouse is a Harem Anime comedy that consists mostly of scenes about hilariously over-the-top heists Sorata pulls and scenes where his accomplices/servants, ahem, lavish attention on him in a hilariously over-the-top fashion.
Tenchi Muyo! Ryo-Ohki OVA - is a series about one guy living with five girls, who're all in love with him consisting of: Ryoko, Washuu, Ayeka and Sasami, and Mihoshi.
- Along with the other Tenchi stuff, there's Tenchi Muyo! GXP. By the end, it's the captain, eight girls and an overpowered starship fighting pirates.
- And Tenchi Muyo! War on Geminar, in which Tenchi's little brother has gathered a half-dozen or so mech pilots around him -- and is actively pursued by at least a hundred other girls who are also all mech pilots.
Rosario + Vampire: All the harem members are capable of holding their own in battle and spend much of the first season defending Tsukune. Justified in that while Tsukune is human, the girls are all Cute Monster Girls - the possible exception is Moka, who needs Tsukune to take off her rosario in order to fight at full strength but even without that she is pretty strong. The show, while very fanservice-y, does also have a strong focus on romance especially in later arcs.
Aiki features only Action Girls that Joukyuu is training.
Sekirei features a main lead with a harem of busty action girls with elemental superpowers, and was fittingly promoted by FUNimation as "the breast action harem anime of all time".
Ranma ½: Ranma Saotome's Unwanted Harem is full of Hot Amazons and Action Girls. Not surprising, since he lives in a world where everybody gets their own style of martial arts.
Infinite Stratos: As his co-homeroom teacher Maya once stated, with his force of six representative pilots, he has more than "enough to start a war."
Maji De Watashi Ni Koi Shinasai: More true for the anime with Miyako, Wanko, Yukie & Chris already in Yamato's harem from the start, and the Momoyo (and others) in play. In the game, each girl has her own route, though in the Ryuuzetseran route, you get Momo, Miyako, Tasuko & Angel.
High School DxD: The more girls who join in the Occult Research Club, the more girls Ise gets.
Kore wa Zombie Desu ka?: The harem consists of a Necromancer, a Magical Girl, three Vampire Ninja.

Fan Works

In Kyon: Big Damn Hero, we have the Reality Warper, the Human Alien slightly-less-powerful Reality Warper, the tazer-wielding Yakuza Princess, the Time Traveler, the Teleporting Slider....

Film

In Manos: The Hands of Fate, the antagonist has a harem of wives that are ready to fight for him... which apparently includes fighting each other.

Literature

The Wheel of Time has Rand in a relationship with three girls, all of whom agree to share him: Min is a Ladette and a Knife Nut, Aviendha is a Proud Warrior Race Girl who used to be a member of an Amazon Brigade and grew from being an Action Girl to one of the strongest female channelers, and finally, Elayne is a Badass Princess who is also an extremely strong channeler.
A Certain Magical Index: Among the girls interested in Touma are a human repository of thousands upon thousands of spellbooks, the third most powerful esper in Academy City, the fifth most powerful esper, a sword-wielding priestess (who happens to be a saint), one of her spear wielding subordinates, a magical spy/courier who wants to seduce him into working for her country, the pre-teen leader of a magical cabal and a former goddess. It's even Lampshaded; some people are starting to wonder if, with all the powerful women he's recruited to his side, he's setting up some kind of resistance force.

Video Games

Kei from Akai Ito has four women who are seriously interested in her, ready to fight to death to protect her. It's very noticeable because Kei herself is not an Action Girl.
Every party member in Brave Soul except The Hero and his pet dragon is female, and is a potential love interest. Actually, so is the pet dragon.
In Eiyuu Senki, every other character other than the nameable protagonist Harem Hero is female. All of whom eventually fall in love with him.
Shirou in Fate Stay Night, and more prominently in Fate Hollow Ataraxia, has attracted gender flipped King Arthur, a magus who can use all five elements, a girl who possesses a piece of the Holy Grail, Medusa and a homunculus who is the Holy Grail, among possibly several others.
Galaxy Angel features Mission Control Takuto Myers in command of the Angel Squad.
In Galaxy Angel II, Shiranami is a pilot and leader of the Rune Angel Squad.
In Koihime Musou, Kazuto's generals do all the fighting.
The Valkyries of former Training Squadron 207B form Takeru's Battle Harem. Mitsuki, Haruka and Akane would have been the same for Takayuki, but the fact that he died even before the three could join VF-A01 kind of precludes that. The Day After has VF-17 "War Dogs" as Hibiki's, while Total Eclipse's Yuuya has Yui, Cryska and Inia, Cui Yifei and possibly Tarisa, although they belong to different military units, and only got together due to their participation in UN's Project Prominence.
Princess Waltz The 2nd Act has all the princesses coming together to face the big bad. They are effectively Arata's harem at this point.
Rance of the Rance series has one of these. The amount of female characters in Rance Quest is immense.
Record of Agarest War has five generations of harem. All of them are Ladies Of War.
An RPG Maker game Romancing Walker has six love interests, and they're all your permanent allies.
In Seinarukana, of the 14 Brigade members, 9 are female. Of these, 6 are potential love interests.
Shiki in Tsukihime, being in the same multiverse as Fate/stay night, has also attracted a harem which includes an ancient vampire who can summon the moon itself, an Executor from the church, a half-demon hybrid, a succubus, an alchemist and an exceptionally powerful classmate-turned-vampire. Also extends to Melty Blood continuity.

Real Life

A male lion will generally have several lionesses in his pride at once.