Alyssa first appears in the Fuuka Academy choir, where she is well known around the school for her wonderful singing voice and is commonly called the "Golden Angel". Mikoto Minagi and Mai Tokiha encounter her on a hillside singing with Miyu Greer during a day off, where they exchange a few words. Alyssa is frequently seen clinging to Miyu, and rarely speaks unless spoken to, coming off as very shy and timid. She is in the Fuuka elementary school.

Later, she is seen summoning an Orphan with Joseph Greer by her side, which causes her to collapse from the strain of it. She is formally introduced as an antagonist monitoring the HiME in episode 12 after Natsuki discovers them to be using the basement of the church as an observation center. The Searrs foundation that she is a part of is noted for influencing many world events (such as the United States presidency) and are responsible for the recent "vampires" plaguing the school, which are actually Orphans taking the blood of female students to find the HiME. Searrs' Board of Directors, with Alyssa's adoptive father as the CEO, plan on seizing the power of the legend of the "Battle Princesses" to usher in their own version of a "Golden Age".

Alyssa was part of a genetic engineering program to produce a "fake" HiME, of which she was the only success (the tag on her foot in a flashback lists her as "Valkyrie No. 143"). Miyu was a super intelligent android created by Joseph Greer to be her guardian, as she was unable to summon an element since she was not a true HiME. However, Alyssa's glowing hair briefly allows her to distract the HiME pursuing her and can seemingly be used to teleport herself and Miyu away from danger. Her hair glows whenever she summons an Orphan or uses any of her "fake" HiME powers, including calling her Child.

After the location of the observation is discovered and the vampiric Orphan is defeated an angry Joseph Greer is dismissed by Alyssa's father (with Miyu acting as a communication device) and he leaves only after realizing the secret codes he installed in Miyu have all been removed.

When the Searrs foundation begins its invasion of Fuuka Academy Alyssa and Miyu attempt to capture Mashiro, only to find that the headmaster had used a decoy and already escaped. In a final confrontation her Child is destroyed by Kagutsuchi and Mai after they leave the atmosphere to protect the other HiME, and Alyssa collapses as her most important person (revealed to be her father) disappears at the Searrs headquarters, where the remaining members comment that they have to wait another 300 years to try again. Miyu carries away the weakened Alyssa, but she is found by Joseph Greer, who shoots Alyssa under orders of the Searrs corporation for her failure. After assassinating Greer in retaliation, a distraught Miyu cries that the golden light she loved has disappeared and carries Alyssa's body into a frozen lake, where it is assumed Miyu herself perished.

In episode 23, it is revealed that Mashiro recovered Miyu (but not Alyssa) and a great deal of Joseph Greer's Searrs technology to repair, and even reformat, Miyu. Midori wakes up Miyu, who then escapes and later confronts Nagi in the library to gain access to the hidden underground cavern of the HiME.

A small presence in the form of a flame that spoke with Alyssa's voice activated Miyu's "Platinum Mode" and anti-Materialiser weapon during the final battle. In the end Alyssa is revived by Mashiro with the other HiME. It is assumed her father was also resurrected with the other Most Important People of the HiME, though Alyssa's specific resurrection is not shown on screen.

Her child, Artemis, takes the form of a huge satellite orbiting the Earth that can fire a massive energy beam capable of destroying bridges, as well as launching a swarm of missiles for point defense. This was Searrs' plan to wipe out the other HiME, leaving Alyssa as the Festival's winner; then Artemis would destroy the Black Prince as well, leaving Searrs with a fully functional HiME and Child for their Golden Age.

The song Alyssa is seen singing is titled "It's Only The Fairy Tale", which is an "Engrish" rendition apparently about the HiMEs, as the lyric "Who are those little girls" and "Twelve of them" refer to the fact that there are 12 HiMEs; all of which are female.

My-HiME manga

This version of Alyssa is actually the younger sister of Natsuki Kuga having been artificially created from her DNA and the DNA of the Searrs president, and while she is still protected by Miyu her personality is much more playful and child-like, and she enjoys glomping her sister. Her child is a floating orb-like machine called Isaac that can manipulate gravity, and instead of glowing golden her hair turns jet black like Natsuki's when her powers are activated. She is also not a member of the school choir and does not sing at all.

My-Otome anime

Alyssa as seen in flashback in My-OtomeAlyssa appears as a flash back in Miyu's memory during episode 24. She is the ancestor of Rena Sayers and Arika Yumemiya; as well as Miyu's creator (who in this universe is known as the Merciful Intellegential Yggrdasil Unit). In the flashback, she is depicted slightly older than her My-Hime version, but with her trademark hairstyle. It is likely that "Sayers" is a phonetic derivation of "Searrs" that occurred over time. Arika's hair glows in the same manner as Alyssa's when she activates the ultimate weapon of her robe, the Sword of Akatsuki, and that when Miyu looks at Arika or seemingly any descendent of her creator she sees glowing hair.

Miyu is almost always seen with a small yellow bird named Alyssa, who shares her human counterpart's hairstyle. Miyu is able to team up with the bird (who somehow carries the genetic imprint of Alyssa Searrs, as Miyu's start-up screen indicates) and execute attacks with her "Maria" sword arm as well as "Artemis", an energy sword slash. In the activation process of Miyu's sword, Alyssa's name is spelled 'Alissa', suggesting that in the Otome Universe, her name (as well as the names of several other characters) has been romanized differently.

My-Otome manga

Alyssa Kruger to the left, Alyssa Searrs to the rightAs in the manga adaptation of My-HiME, this Alyssa is also Natsuki's younger sister. She first appears in Chapter 14 and shows off her intelligence, as well as being critical of the Otome system. She wants the Otome replaced by the MAIDs, a series of intelligent androids based on Miyu, a proposal that is rejected by Natsuki. It is learned that she wanted Natsuki to go back to Aries, something that Natsuki had not done in a long time. She has Miyu challenge the Otome and the MAID proves superior in all but combat abilities but Natsuki protects her sister satisfying Alyssa that she is still loved by her older sister before she and Miyu return to Aries. She wears a clip in her hair identical to the one worn by Natsuki, suggesting that perhaps it is a family symbol. Their mother Saeko Kruger is also shown wearing a similar clip in Chapter 15.

Later another Alyssa appears, this one being the last HiME revived by Mashiro. She tries to bend Miyu to her will using a gravity altering device, but this fails. Instead of separating Miyu and Kruger as Searrs desired, the two manage link hands after a struggle against the increased gravity, restoring Miyu's old memories and "unlocking" a new form of the Mythril Dress for Miyu. With this new power, Miyu attacks Alyssa Searrs, who becomes the first of the HiMEs to be defeated