The Dere-Dere: Why Are They so Easy to Love!
The dere-dere is defined as a 'love struck' character. In other words, someone with a lovey-dovey personality. She is usually gentle, compassionate, sympathetic, and kind. Unlike the tsundere, she doesn't mask her feelings to the protagonist by acting rude towards him. A dere-dere may act maternal, wanting to be the caretaker of their love interest. Sometimes, their good natures make them a target for bullying by rougher characters. They may be naive or too innocent at times. But they're certainly charming because of the way they stick to high moral principles like compassion even in the face of others mistreating them.
Related Character Types:
I am 16, going on 17, I know that I'm naive...
Fellows I meet may tell me I'm sweet, and willingly, I'll believe...— '16 Going on 17' - The Sound of Music
In Western theater and literature, the 'ingenue' is a character type marked by cuteness, youth, purity, and innocence. She is sometimes contrasted with a more sexual, and darker, and more mature, foil character. This dichotomy is brilliantly deconstructed by the film Black Swan.
A 'Mary Sue' is a character type often criticized as a poorly written (female) author-insert character, who lacks character development because of her unrealistic perfection. An irritating thing is that this total perfection in reality is something the author attempts to mask with flaws that aren't really flaws - like being 'too nice' or having a physical 'deformity' that actually makes her cuter, or is barely noticeable. Or with fake humility - a Mary Sue will often have nothing physically wrong with her and, in visual media be very attractive, but she might stand in front of a mirror pouting about minor imperfections in her appearance.
In Japanese fiction, the Yamato Nadeshiko is the traditional Japanese housewife/mother type. This also corresponds to the Jungian 'mother' archetype said to permeate all of human fiction. Since we're mostly talking about anime, which is usually written for and about teenagers, it's not a literal mother. Instead, it's a character who has traditional graces and manners, and acts warm and maternal, especially towards her love interest. Expect this character to be a good cook and good at household cleaning. This is often shown in contrast to a more tomboyish or carefree girl, who is not.
The 'Manic Pixie Dream Girl' is a somewhat newer phenomenon, largely in Western film. This is a girl who comes into a male character's world to brighten it with her youthful, energetic, optimistic, quirky outlook on life. Then she usually dies or goes away or something. This character type has been blasted and parodied on the internet a lot, like with this YouTube series, the Manic Pixie Dream Wife.
The 'dumb blonde' is a related trope, as is the common media association of blonde hair and blue eyes with purity and innocence. That's why many of these examples are blonde.
Major Anime Examples
Vash the Stampede from Trigun is a male dere-dere. He clings to his principles which include compassion and non-violence, even in the face of pain and suffering.
Pictured above, Pacifica in Scrapped Princess. Similarly, she endures a lot of suffering and persecution, but maintains her sweetness and belief in the good in people.
Sailor Moon is a dere-dere, deeply concerned about the suffering of others. Her viewpoint is considered naive and childish by older characters, Sailors Neptune and Uranus. But Sailor Moon will do anything for the people she loves and her friends.
Brock from Pokemon is another male example, although his problem is that he seems to be more in love with love than with the people he falls for (once an episode, or near enough). But inside, he is a deeply compassionate person, who loves taking care of Pokemon and small children.
Holo, from Spice and Wolf. She's introduced in such a way that you might expect an arrogant 'kamidere' type. But she's actually a sweetie, and she deeply yearns for companionship, though circumstances forced her into isolation. Lawrence is in a similar boat, which forms the basis of their friendship and romance.
Tohru Honda in Fruits Basket, whose inspirational kindness in the face of adversity brings out the best in even difficult characters.
Madoka in Puella Magi Madoka Magica. This is by design, it's a deconstruction of the Magical Girl genre, and Madoka represents the purity and naivete of traditional Magical Girl protagonists. Mami also embodies this trope, with her blonde twin drill hair representing her innocence and princess-like qualities.
Why is the Dere-Dere Appealing?
They don't play mind games or manipulate people. They're neither violent like the yandere and tsundere, nor cold like the kuudere. This is perhaps the easiest of all types to understand the appeal of, they're sweet and loving! They give us hope and inspire us. Winning them over is also easier, you just have to be a good person. These characters are also often victimized by meaner characters, which makes us feel sorry for them. That awakens our big sibling instinct - we want to protect or save them because they're so pure and good.
Examples of Dere-Deres Outside of Anime
Maria from Sound of Music.
Mary Poppins from the Disney movie, but I've heard less so in the book.
Disney princesses, especially the older ones like Cinderella and Snow White. Also, many prominent female Disney characters who aren't princesses, like Lady from Lady in the Tramp and Maid Marian from Disney's Robin Hood.
The Virgin Mary from Christianity. Most female saints as well, taking her as a role model.
Princess Cadence in My Little Pony: Friendship is Magic. That's how Twilight is able to spot that the changeling queen pretending to be Cadence is a fake - the imposter lacks Cadence's kindness and heart.
Marge Simpson. Being this type can suck sometimes.
Luanne from King of the Hill. Who is often targeted for manipulation by others because of her naivete.
When badly written, the whole 'purity and goodness' thing can be over-the-top, which feels insincere, unrealistic, and cloying. Sometimes they can just be boring.
But well-written derederes are easy to root for, or even fall in love with. Audiences like how they 'kill em with kindness', and always seem to overcome their struggles without becoming hateful or using violence. This is the kind of character that is fun to root for.
It's also the kind of person we're most likely to want as a friend or romantic partner in real life. We might find the animalistic craziness of the yandere hot, in fiction, but we would get a restraining order against someone like that in real life! Not so with the deredere, proving that nice girls (and guys) don't always have to finish last.