Not cause of how they perform in battle. But really cause how they act in general. Generally its always, "I must save/protect this girl cause she's the key to saving the world or destroying it." When you first meet them they're generally in trouble. You save them then they kindly leave out the important detail that they're hiding a secret that if you knew beforehand, you could save yourself a lot of trouble. If you meet them at the end of the game. They fall into either give you a kiss and you lived happily ever after or hey guess I'm actually evil.
What's worse is they generally act more helpless than normal. Requiring the main character to jump in make decisions for them not just one time, but on multiple occasions. And generally you hear the words, "I'm sorry" from them often. Really what are you apoligizing for? Did you bring that boss fight to me? What did you do? It's worse when they get really depressed as they tend to either wish that they were dead or attempt to actually kill thereselves. Usually at this point it requires the main character to jump in do something heroic and making the hero fall in love with the princess.
You hope for at that point that everything is over and done with. But often times its not. Why? Cause the same princess who's been rather Helpless and needy. Is the key to saving the world and/or the apocalypse. Even more questing must be done to help her gain the resolve she needs to fight the epic final battle. Well hold up...couldn't we just kill her and save ourselves the trouble? Nope cause at this point you pratically require her to fight with you. In worst case scenario...she's your one and only healer to the group. Meaning she has some value.
You can refer these types of characters to most of the Disney Princesses you see. As they generally do the same thing. Wish for something to happen....a random person idly comes by or some random 1 time event no chance this will ever happen again arrives and they take it. When before they were just generally wishy-washy. Did they work for that dream....some cases yes....but often times no.
Honestly this type of character is just annoying. Granted they try as signs of growing up. But its generally towards the end of the game that they finnally grew a backbone. I'm generally tired of saving there behinds or saving the world from the brink of destruction cause your helpless yet you have all this power. Oh but they don't know how to fight. Just makes it worse. Now I gotta protect you even further.....more tedious questing. Can I save the world without having to save a princess on the side?
Examples of the Helpless/Useless Princess Character (spoilers)
- Luke Fon Fabre (Tales of the Abyss) : Although not a female. Often through the story you find him feeling sorry for his self. He comes back with new resolve but quickly falls back into depression. Luke finnally has a true resolve at the end but ends up sacrificing his life anyway to save the world. It was the main thing the party told him not to do many times. At least it wasn't due to depression but still.
- Estelle (Tales of Vesperia) :When you first meet this chick its very simmaller to a group muggers after a lady. She kindly leaves out the fact that she's a princess (although Yuri shoulda figured that out beforehand.) When we finish with her task we find again not 10 minutes later wanting to cling to Yuri and the party. We later find out that her power is rather unnatural but it harms the world despite how much she likes to "help people". She goes into a depressed state being kidnapped and used as a weapon. Due to being used as a weapon she is used to bring forth the apocalypse although technically she didn't do it herself she is the key to the apocalypse. We also get into battle with her and she wants Yuri to kill her. Although in the last part of the game she develops a resolve to fight and save the world. This all coulda been prevented to an extent by simply killing her....but nope she's the main healer of the group so she's needed.
- Rinoa Heartly (Final Fantasy 8): Up until end of disc 3 she from the moment you meet her in disc 1 she's very clingy towards Squall. Generally unable to act without Squall to help her in some way. She attempts to do things on her own but ultimately fails each time. Requiring Squall to protect her. She falls into a coma at the end of disc 2 requiring Squall to carry her by piggyback to get help from a city that's totally closed off to the outside world. Why cause she gained Sorceress powers which generally end the world. But due to the apparent "love" Squall had for Rinoa. She is saved from being sealed in a chamber for eternity. How did Squall come to love Rinoa is beyond me but she is a key to making the world an apocalypse. And in disc 1 she is generally helpless. Despite being the one that hired Squall and the leader of her rather small group of rebels.
- Dominique Cross (The Bouncer): Well Dominique does pose immediately as a helpless little girl with tough friends. And she's rather flirty. The minute the game begins she is kidnapped. The heroes go to great lengths to save her only to find out she's a sister to the final boss of the game. What we find out a few minutes later into the game is that she's an android. A very powerful android. But doesn't know of her power. What's bad is that she is the key to an evil satellite that the final boss used to blow up a hospital. The final boss's intent? To get revenge on ppl that ruined his childhood by blowing them up. Key to apocalypse yet again and helpless. To make it worse there's a level where you must protect her from death. Although her attack power is godly high she does nothing but walk slowly through the stage, following you and standing in areas of danger. If she dies its game over. Great....
- Princess Peach (Various Nintendo Games): You see this chick in 1 of 3 ways. She's either the damsel in distress requiring Mario and his Bro to go through 8 castles to save her. She's a playable character showing off what she can do to try and have the tough girl act. Or its both. Either way she's generally in danger. Luckily she's not a key to saving or destroying the world.
- Atoli (Dot.Hack//GU series): Pretty much the opposite of Haseo's previous love interest. She's needy, clingy, has healing powers, but more importantly she plays a key role to the story as being an Epitaph user. Although you can't blame most of her actions on her alone. Haseo pretty much ignores her for most of the game which pushed her further into depression. She ends up being a rather annoying boss fight constantly yelling about wanting ppl to look at her and not to look at her. What's worse is she won't shut up about it until you beat the crap outta her.
- The Maidens in Musashi Samurai Legend: This one is kinda of a gimmie. But they all qualify. Each and everyone of them requires you to find them in the middle of nowhere and bring them back home. By carrying them. You have to carry them cause they suddently lost there ability to walk. This would be cakewalk but the moment you pick them up the enemies pretty much chase after you like you owe them money. Yes even you too Istara. It doesn't help that most of them are rather plain out rude to you for carrying them making you wanna drop them down a cliff. Add to the fact that you can't properly fight back against them making the game rather frustrating at times.
- Kairi (Kingdom Hearts): Doesn't help that she's counted among 6 other princesses that are from disney. But up till you reach Hollow Bastion you're pretty much searching and fighting to save Kairi....Yeah yeah protecting the worlds from darkness as well but Sora's intent is to save Kairi. Granted that she's in a comatose state for most of the game. She is one of the keys to bringing forth destruction to the world. It doesn't help that she's kidnapped in KH2 in order to get Sora do as the Organization wants. She does redeem herself in that game by actually trying to take action. She doesn't act stupid and instantly follow the stranger that comes to her in an alleyway. She actually attempts to fight back even better she gains a keyblade even though having no experience with to protect herself. Still doesn't completely save herself from falling under the helpless princess title.
Too many more to name but those are just examples.