- Voiced by: Takahiro Mizushima (Japanese), Braden Hunt (English)
Takeru Takemoto is the series' main character. He comes off as a lazy and unmotivated teenager, but is really just unsure of his place in the world. He found and named Hikari in the woods in the first episode. After finding Hikari, Takeru gains inexplicable new powers which allow him to transform into a powerful, yet primal being with incredible lethality, but has also been shown to be able to transform into something between his human and monster forms. This power is later explained to be a result of Extended Definition. Takeru eventually develops a love interest in Hikari, ultimately convincing Hikari to spare the world for their love. It is shown that he has some feelings for Mari, but only as a relative. He is obsessed with motorcycles and wanted to take Hikari on a journey throughout the country on one.
- Voiced by: Ayako Kawasumi (Japanese), Cynthia Martinez (English)
A mysterious girl who 'fell from the sky', Hikari fell in love with Takeru at first sight after being found in the first episode. She is very cheerful and thinks that almost everything is beautiful. While she can not remember anything before the day Takeru found her, it is later discovered her purpose is to destroy Earth. She is the goddess of darkness,death, and destruction. Hikari has split personalities, and her appearance changes depending on which one is dominant; her "good" personality is characterized by orange hair and green eyes, and her "evil" personality is characterized by pink hair and red eyes. By the series' end, she decides to destroy the earth, but Takeru stops her with his love for her. In the end of the anime, Hikari instead lives with Akari in the stars, though claims to return someday.
- Voiced by: Fujiko Takimoto (Japanese), Quentin Haag (English)
Ryou Ninomiya is Takeru's best friend and is favored by many of the girls at school because of his gentle nature. He is consistently called "Ryou-sama" by Sakurako and Amika. He is the one who found Akari and throughout the series develops feelings for her. He too develops special powers, his being the ability to grant his wishes, shown by blue spirals on his hands. At the end of the series, he was about to kiss Akari, but his efforts fall short when Akari stops him and says they are family. Ryou smiles and gently kisses her forehead.
- Voiced by: Ai Shimizu (Japanese), Jessica Boone (English)
Akari is a girl that appears just as mysteriously as Hikari. Ryou finds her in the forest and makes her part of his family. She considers Hikari her older sister, and she grows very attached to Ryou and Kimi. Akari later reveals that she and Hikari are actually one being and that they were split into two during their landing. The part of Hikari's personality that doesn't want the earth destroyed is manifested in Akari. In the end of the anime, she and Hikari wander the stars with only each other.
- Voiced by: Asami Sanada (Japanese), Luci Christian (English)
Mari Nishino is Takeru's cousin, While she nags Takeru for various reasons, Mari harbors jealousy of Takeru and Hikari's relationship. Although she denies her feelings for him early in the series, Mari falls in love with Takeru. Throughout the series she is aggravated by the closeness of Hikari and Takeru, and distrusts Hikari, although is nice to her through the beginning of the series. Her jealousy of their relationship grows as her love for Takeru grows largely unrequited. Near the climax of the series, when Hikari attempts to persuade Mari to join her and Takeru on their journeys, Mari slaps Hikari and yells at her, saying that she is a backstabber and an awful friend, ultimately making Hikari change into her "evil" form to destroy the world. She later admits her love to Takeru, attempting to make him not follow Hikari, but Takeru only smiles, thanks her, and goes to persuade Hikari to spare the world.
- Voiced by: Yumi Takada (Japanese), Shelley Calene-Black (English)
Jennifer Portman is a crazy American super-scientist who came to Japan to study the "Extended Definition", a species' ability to prevent its own extinction, which usually manifests itself in said species transforming into a monstrous form that maximizes its combat potential, and gives it the instinct to attack or kill Hikari. She moves in with Takeru, Hikari, and Mari. She's rarely to be seen without some kind of alcohol and is somewhat of an exhibitionist. Although out of work she appears ditzy and idiotic, she is extremely intelligent at her work. Her personality is seen as a blend between that of Misato Katsuragi and Ritsuko Akagi from Neon Genesis Evangelion (another Gainax series).
- Shinichi Voiced by: Atsushi Kisaichi (Japanese), Robert Martinez (English)
- Daijiro Voiced by: Hideki Ogihara (Japanese), Chris Patton (English)
Shinichi Asakura and Daijirou Matsumura are schoolmates of Takeru who seem to always be dreaming up some kind of perverted fantasy, especially once they met Hikari.
- Sakurako Voiced by: Manabi Mizuno (Japanese), Lesley Tesh (English)
- Amika Voiced by: Yumi Kikuchi (Japanese), Taylor Hannah (English)
These two girls love Ryou, calling him "Ryou-sama" or "Ryou baby" in the english dub. They made Hikari's and Akari's clothing. They also enjoy egging on the love triangle between Takeru, Mari and Hikari.
- Itcho Voiced by: Dai Matsumoto (Japanese), Bob Parke (English)
- Sumie Voiced by: Tomoko Kotani (Japanese), Anne Armogida (English)
Itchō and Sumie Nishino are Mari's parents. They took in Takeru when his mother abandoned him at a young age. Currently, they run two business ventures: a delivery business and a boarding service.
- Voiced by: Emi Kobayashi (Japanese), Hilary Haag (English)
Kimi is Ryou's loud-mouthed younger sister who takes care of the housework when her brother is out. She was the only person living with Ryou until Akari came. She seems to be very protective of Ryou and, while she allowed Akari into their home, attempted to put a barrier between them and frequently got mad whenever they came into close contact.
- Voiced by: not available (Japanese), Greg Ayres (English)
Kuon is the little creature that takes care of Akari. He looks like a specter with two luminous eyes but no defined body shape, except by his clothing. He is capable of levitation and apparently has some sharp tentacles, as he is seen carrying a watermelon with them which he later uses to remove the rind from the watermelon. Towards the end of the series, Kuon and Ioneos enter hibernation mode and become a crystal. Kuon becomes a chip of the crystal which is probably why Kuon was small and Ioneos was big.
- Voiced by: Keiichi Noda (Japanese), Paul Oddo (English)
Ioneos is like Kuon's "older brother," as he and Kuon are created from the same type of magical crystal. However, Ioneos's appearance and size are much larger and sleeker than Kuon's because he is an entire crystal, save a small chipped fragment which Kuon is made from. He was sealed inside of one of the school's stone pillars until Hikari accidentally released him during a routine fire drill. The entire school was subsequently demolished after the blast following Ioneos's release. Jennifer nicknamed him "Oniita," (or "Neo" in the English dub) saying that his original name was too long. In the end, Ioneos enters hibernation mode along with Kuon and become crystals, Kuon being the little chip and Ioneos being the big crystal. Jennifer puts them on a necklace and wears the crystals.
- Voiced by: Mai Kadowaki (Japanese), Monica Rial (English)
Mayu is the class representative. She is short and full of self-doubt. In one episode, Mayu admits to Hikari that she sometimes hates school because everyone teases her, which makes Hikari turn into her "evil" self and destroy the school (brought on by Mayu's hate for school) although Mayu does not seem to remember it.