Koushiro "Izzy" Izumi

Koushiro "Izzy" Izumi (泉 光子郎 Izumi Kōshirō) is a character in the anime and manga series Digimon Adventure and Digimon Adventure 02.

He is partnered with Tentomon. Izzy is a computer nerd and spends all his time trying to figure stuff out on his "PiBook" laptop. He played on the soccer team with Sora Takenouchi and Taichi "Tai" Kamiya (Taichi Yagami in Japan). Izzy lives with his adopted parents. When he initially found out, he began to subconsciously distant himself from his parents and focusing on his computer. The issue is resolved when his parents come forward with the truth and he accepts them as his true parents.

He is the bearer of the Crest of Knowledge. He is one of the core members of the DigiDestined in both seasons. His color is purple and element is electricity. He is voiced by Mona Marshall in the English version and Umi Tenjin in the Japanese version.

Prelude to Digimon Adventure
He saw the battle between Parrotmon/Greymon, resulting in him becoming a DigiDestined.

Digimon Adventure
Izzy is the computer whiz of the group, most curious of the Digital World. He often prefers to be alone; he is still in his cabin after the snowstorm, still trying to connect with his infrared connection. Tai has to yell to get him to step outside. Once in the Digital World, Izzy develops an "alien theory" and has a low opinion of the Digimon. For instance, he says, "We should go find intelligent life." Biyomon says, "Sora, is Izzy saying that we’re not intelligent?" His partner, Tentomon, also wonders about Izzy’s alien theory, saying, "What mystery is there to me? I am who I am." When the DigiDestined enter a factory, Izzy finds a large battery and enters. He wipes away a part of the hieroglyphics on the inner wall, causing the factory to stop production. Izzy becomes the first to realize that everything, even the program, is living in the Digital World.

Izzy’s skills with the computer, however, soon prove to be extraordinarily useful for the group. During the battle against Andromon, Tentomon suggests that Izzy reenter the program that activated his Digivice. When Izzy retypes it in, Tentomon digivolves into Kabuterimon and defeats the black gear in Andromon. When Mimi and Tentomon run into a maze, Izzy pulls out the map and locates Mimi’s location. He then directs her out of the maze.

After the defeat of Devimon, the DigiDestined are sent to the continent of Server to defeat Etemon. While they are in the capacity of Piximon, Matt and Izzy see that their tags are glowing. They sneak out and find their crests; Matt receives the Crest of Friendship, while Izzy receives the Crest of Knowledge. Izzy’s curiosity and deductive reasoning comes in handy once again; when Datamon captures Sora, he is the first to theorize that Datamon is still inside the pyramid. Tai and Izzy rescue Sora. Etemon learns of their prescence and goes down there to destroy those kids. In the final ensuring battle, Greymon successfully digivolves into MetalGreymon and defeats Etemon. Tai and his Digimon are sucked into the Real World; during their short stay there, Izzy sends a frantic transmission, warning Tai not to go back to the Digital World.

However, Tai reenters the Digital World anyway, because he knows that he must restore the balance between the two worlds. Izzy runs into Vademon, who tricks him into giving up his curiosity and regresses him to an accepting mind that does not question anything. Tentomon frantically tries to get him back to no avail; he slowly reverse digivolves back into Motimon and Pabumon before Izzy snaps out of it. Izzy gets his tag and crest and his curiosity back. In the ensuring battle, Kabuterimon digivolves into MegaKabuterimon and defeats Vademon.

During the search for the Eighth Child, the DigiDestined pursue Myotismon into the Real World. Gennai loads a couple of programs into Izzy’s laptops that gives him much information. The first program tracks the movement of Digimon; Izzy sees Raremon attacking Tokyo Bay and rushes out there with Tentomon to stop him. The second program puts up a digital barrier, which stops the Bakemon from taking Izzy and his parents away. Gennai also tells Izzy that the source of Myotismon’s power is in the Fuji TV station and describes the prophecy to him. The prophecy aids them in defeating VenomMyotismon; when Izzy reads the prophecy out loud, the group follows its lines. Angemon and Angewomon hit Matt and Tai with arrow of light, which leads to Agumon and Gabumon warp digivolving into their Mega forms. Their Mega forms aid tremendously in the battle.

During this saga, Izzy’s parents reveal to him that he was adopted. Izzy’s real parents were killed in a car accident, and his father’s brother adopted Izzy. Izzy also reveals that he found out when he overheard a late-night conversation, and says that he retreated into computers to try to forget about what he had overheard.

Izzy’s computer becomes a more valued asset as the DigiDestined battle the Dark Masters. Before, their Digimon partners used to describe the information about the various Digimon that they encountered; now, Izzy has loaded a database of Digimon profiles. When a new Digimon shows up, Izzy names and describes the characteristics to the rest of the DigiDestined.

In the last battle against Piedmon, Izzy was turned into a keychain. After Apolaymon was defeated, Izzy calculated that, because one day in the Digital World equaled just one minute in the Real World, the DigiDestined could stay in the Digital World for 118 years. However, Gennai tells them that the time distortion was fixed with the defeat of Apolocymon, and that the solar eclipse would seal the barrier for an indefinite amount of time. Izzy says goodbye to Tentomon, thanking him for being a good friend.

In May 2000, Izzy arrived at the Digital World and gave up his Crest power to free the Sovereigns. As a result, Tentomon lost the power to become MegaKabuterimon.

Digimon Adventure: Our War Game
In Our War Game, Izzy is the one who first discovers a digi-egg infected with a computer virus on the internet, and then rushes off to alert the others. At first only successful in finding Tai, he plays a key role as the brains behind the attacks that were implemented by Tai and Matt.

Digimon Adventure 02
Three years later, Izzy is now in high school (middle school in the original vvrsion) and was a highly-regarded president of the Computer Club. Izzy continues to play his technical role; he monitors the Digital World and alerts the new DigiDestined to upcoming troubles and problems. Izzy devises the plan to invade Ken’s base; with Cody’s information that a pipeline will cross paths with Ken’s base, he directs Agumon and Gabumon to create a diversion. Later, when Ken’s base is about to explode, Izzy tells them the problem and when the warp is back to normal.

With Willis from America, he also figures out that the new Digivices have three new functions, and dubs them the D-3s. Lastly, after school gets out, Izzy theorizes that the power of the D-3 is what really opens the gate to the Digital World. This theory proves to be correct, and gives the DigiDestined the ability to open up ports at any time and any location, rather than being limited to simply using the school’s computer lab to move in and out of the Digital World.

By the year 2027, Izzy sets up a research team to study more of the Digital World than what the human population already knows. He has a daughter, with a Motimon, but her mother is not revealed.

Digimon 02: Diaboromon Strikes Back
Like in 'Bokura no Wargame!' Izzy still was responsible for the planning and execution of the attacks on Diaboromon. He was the one who gathered all the Chosen Children (including Tachikawa Mimi flew in from America) to help defeat Diaboromon and stop the havoc it wreaked on the net and the real world.

Trivia

 * Izzy carries with him a yellow laptop that has a pineapple on it, a likely reference to the iBook considering its appearance and the fact that in the manga of Digimon Adventure, it is referred to by name as a PiBook. Several images of the screen of Izzy's computer also resemble the Mac OS. (In the second Digimon movie, all the computers featured Windows screen shots because a different animation studio was used.)
 * During Anime North 2006, Jeff Nimoy, a writer for the English dub, claimed that he used the personalities of gay lovers for Izzy and Tentomon.
 * Izzy has two Japanese image songs, "Version Up" and "Open Mind," as well as a third one sung with Tentomon called "Sekaijuu no Keshiki wo!" ("The Scenery of the Whole World!").