Sera

Sera (セラ) is a character from Mega Man Legends 2, the Mother Unit who rules over the systems on Elysium. Sera is serious and machine-like in personality, and does not understand why the Master trusted Mega Man so much, following the System strictly. She is accompanied by her Servitor Unit named Geetz. She is the sky goddess who "guards the record of the ages."

Story
Several years before the events of Mega Man Legends 2, after the Master's death, Mega Man Trigger fought against the System to destroy it and fulfill the Master's dying wish, fighting against Sera, Yuna and unknown others. After Yuna decided to take a neutral position in the battle, Sera was frustrated with her decision and traveled to Terra herself to fight against Mega Man, and the two fought each other to a standstill as she wasn't able to bring her full power to bear outside of Elysium, both expending all of their energy and Mega Man's original body almost totally destroyed. After the battle, Yuna took that opportunity to seal both inside stasis fields, with Sera being imprisoned on Forbidden Island while Mega Man was "reseted" and was sealed with Data on Nino Island.

In Mega Man Legends 2, Sera and Geetz where freed by Mega Man when he went to the Forbidden Island, not knowing it was her as he lost his memories, and they pretend they don't know who he is. Sera and Geetz where taken to the Sulphur-Bottom, where Geetz says to Von Bluecher they need four keys to unlock the Mother Lode, which will allow them to have access to ancient technology and produce any amount of Refractors, and by Bluecher's request, Mega Man searchs for the keys. After Mega Man obtained the last key, Sera and Geetz attack the Sulphur-Bottom and steal the keys, which are needed to open the Library in Elysium and execute the Carbon Reinitialization Program. Sera leaves to Elysium while Geetz tries to take the Master's Genetic Sample from Mega Man, damaging him in battle. After being repaired, he went to Elysium to stop Sera. In the Library on the Mother Zone, Sera says she could already have started the Carbon Reinitialization Program, but didn't because it would be beyond the System's limits, and doesn't understand why the Master attempted to destroy the System, and is jealous of Mega Man for him being the closest to the Master and able to understand his thoughts in a way she wasn't able to. She waited for Mega Man to defeat him, hoping that it would purge herself from her "troublesome emotions". Some time during the fight, Gatz tries to help Mega Man by invading her internal systems, but his sabotage attempts where not able to even damage her. After this, she changes to a larger form with wings. After Mega Man defeats her and she starts to faint, Sera says the more she obeyed the system and tried to serve the Master, the sadder he seemed when he looked at her, and now, thanks to Mega Man, the Master whould probably also smile to her as he did to him, as she finally understand what they wanted, at least a little. Yuna (in Matilda's body) appears and ask Sera to transfer her primary program over to Yuna's original body before her shell stopped working to save herself, saying Gatz had died because of her "gamble", and if she also dies, there would be no one to keep her company, and now that Elysium is no longer functioning, the old System the Master's people shut down has started to reactivate, being Sera's responsability to monitor it, and if she die and it takes over Terra, the Master's sacrifice would be for nothing, convinving her to save herself in Yuna's body, with Yuna commenting she doesn't remember the last time Sera smiled. Sera, Yuna and Mega Man need to return to Terra, but the game ends with them trapped in Terra, with no means to return.

Trivia

 * The word "sera" is Italian of evening. The word "serenade" comes from the word "sera" since a serenade is sung in the evening.
 * It's believed the character Serenade.EXE from the MegaMan Battle Network series was based on Sera.