ZERO

E-100 Alpha (Ｅ－１００ “アルファ”), also known as E-100α and ZERO, is a minor character in the Sonic the Hedgehog series who first appeared in Sonic Adventure but plays a major role for Amy. It is the prototype model for Dr. Eggman's E-100 series of robots, which has earned it the designation as the zeroth E-100 unit. During its last mission to recover Chaos Emeralds, ZERO relentlessly pursued Amy Rose for the Chaos Emerald she unknowingly had until it had harassed her to the point of being on the receiving end of Amy's hammer.

Appearance
Unlike the E-100 Series robots, it does not have "E-100" on its body, but instead it has "E" on both sides of its body. Also, the headlight on ZERO is on its shoulder, in contrast to the E-100 Series robots in which it is on their mid-section.

History
In Sonic Adventure, ZERO made its debut by chasing a blue Flicky in the possession of a Chaos Emerald that has taken refuge with Amy Rose. ZERO chased Amy around Station Square, Twinkle Park, the Egg Carrier, Hot Shelter, and finally, the Final Egg base in the Mystic Ruins.

When it went back to the Egg Carrier, it saw Amy and the Flicky with the bird's relatives, who were inside E-101 Beta and E-102 Gamma. ZERO then attacked and knocked out the small Flicky with an extending punch. Amy, thinking that ZERO had killed her companion, became furious and attacked ZERO - finally destroying it by knocking it into an electric fence, scrambling its circuits, before smashing the vulnerable circuitry in its head with her hammer, causing him to explode.

Sonic Advance 2
ZERO makes a brief appearance in Sonic Advance 2, chasing the player around the Special Stages of the game. In this appearance, it is known as the Robot Guard (ガードロボ), but otherwise looks identical to its previous appearance. If it hits the player, they lose ten rings.

Sonic Rivals 2
ZERO appeared in Sonic Rivals 2 as collectible card No. 81. It was unlocked by obtaining the high score in Zone 6 Act 3.

Personality
ZERO pursues its target with a single-minded tenacity, even after the Flicky's Chaos Emerald had been removed. This also made it possible to trick it, as Amy could hide beneath barrels or around obstacles to elude it. When pushed to the brink however, it becomes much more aggressive.

Powers and abilities
ZERO differed greatly from the other E-100 robots as it lacked a projectile weapon of any sort, mainly relying on locking onto an opponent and launching its fists to attack its foes, which functioned with a lock-on system and tethered hands. Unlike the standard E-series model, ZERO lacked legs or a Jet Booster, instead relying on a built-in propulsion unit for locomotion, which helped it to move over any terrain possible. It possessed impressive strength, able to smash through walls in pursuit of Amy and generate shockwaves by punching the ground. It also had strong defensive strength, as Amy could only inflict damage by electrocuting it. It also seems to possess an "overdrive" mode after taking a certain amount of damage, where steam begins bellowing from its smokestack-like head, rendering it invulnerable to any sort of blow from the Piko Piko Hammer.

Boss guide
Amy ends her adventure by battling ZERO at the Egg Carrier's deck as the final (and only) boss in her storyline.

During the battle, the player has to knock ZERO against the electric ropes that encircle the boxing ring. When Amy swats ZERO into the hot wires, its body gets an unhealthy jolt, and the top of its green noggin flips back to reveal a big, blue core. The player gets change to do damage on ZERO and he then flips back his green top to cover its core. ZERO then starts attacking with shock waves, as the player has to keep distance between ZERO and Amy to hop over them. When ZERO's almost finished, it sends an electric "jump rope" after Amy, which she must skip to survive. Run along in the same direction that the rope is turning and jump to easily avoid it. After doing four hits to its core, ZERO finally explodes into pieces and the player has cleared Amy's storyline.

Sonic X
ZERO also appeared in the anime series Sonic X, in the Chaos Saga. His role in the series mirrors to that in Sonic Adventure.

Trivia

 * Alpha is the first letter of the Greek alphabet. Similarly, Zero (AKA Alpha) is technically the direct predecessor of the E-100 Series robots.
 * It is never explained as to why ZERO continued to pursue Amy Rose and the Flicky Bird after having successfully captured them once before. As the Flicky was no longer carrying a Chaos Emerald, and Eggman would have had no need to re-capture Amy, it is possible ZERO was only possible of following the most basic commands, and never received new orders after completing its original mission.
 * ZERO is not powered by an Animal like its immediate successors, as nothing is seen escaping from its body after its destruction.
 * Although it is not called an E-Series robot in the games, it was given a similar codename on the Sonic Adventure website accessed via Dreamcast.
 * Despite this, Eggman apparently does not consider ZERO to be a part of the E-100 Series, as he calls E-102 Gamma his second model.
 * ZERO, E-105 Zeta (the second form), E-121 Phi and E-123 Omega are the only earlier E-Series robots that do not follow the same basic design as E-101 Beta.
 * As a villain, ZERO has traits common to the Strong Silent Types of "slasher" movies in that it is big, slow, strong, and cannot be hurt or killed under normal circumstances.
 * On the early Japanese Sonic Adventure website, ZERO is dubbed the "Prototype of the Eggrobo E-Series" (エッグロボＥシリーズの試作機). It is uncertain if this is supposed to be meaning behind the "E" in E-Series, if it was actually intended to be a throwback to Eggrobo, or if this was outdated information by the game's final release.
 * ZERO is sometimes known among fans as "The Chase Master" due to the name of its song on the soundtrack.