Chirper characters are characters that appear only as Chirper icons. They pop up on the map, and when you click on them, they will say a little bit of random nonsense before disappearing into the ether. They all say different things, but each character has a distinct "flavor" and will always say things of a certain nature. For more details, simply read the descriptions of any of the characters listed below.
While Chiper characters only appear as Chirper icons, any other character in the game (such as Histoire) can also appear as a Chirper icon, in which case they can be clicked to spout more nonsense. In rare occasions, this can actually nail you a cutscene, and in even rarer occasions, you might actually get an item or something.
Additionally, many plans are recieved by talking to Chirper icons.
Chairwoman of the Nep FanclubNeptune fangirl, and the leader of the bunch. She has quite hairy legs, which she does not shave, much to the disgust of her fellow fanclub members.
Fun fact: Some Japanese hiki-NEETs really do use the "home security" excuse to justify their positions, which is what the character is based on. They do so jestingly, or at least I hope they do.
KeppyKeppy knows! Neptunia is a shit franchise.
Ms. ManualHistoire already has plenty of more in-depth tutorials that are actually somewhat useful. Ms. Manual is single and has never been married.
NepugiaNepgear's doppelganger. She's a cute girl with oversized bangs that block her eyes, and a black outfit that's very similar to Nepgear's. It's not known why she impersonates Nepgear. Maybe she's actually a big fan? She's known for her famous line, "Hah! Didja think I was Nepgear? Too bad! It was me, Nepugia!" Often times she teases the player with fanservice, only to reveal the obvious, which is that she isn't actually Nepgear. While her hairpin may make her seem like she's a devious member of ASIC, she's actually a real sweetheart.
Snake HayterIt's Snake.
By the way, the box he's hiding in is a mikan box (mikan is basically a Japanese orange). Mikan boxes are a common gag in anime, and can be seen as background (or foreground) objects everywhere, especially in slice of life anime/anime that take place in the real world. If there's ever a cardboard box in an anime, odds are it's a mikan box. He is usually associated with Lastation.