Sonia Strumm, known as Hibiki Misora (響ミソラ Hibiki Misora) in Japan, is a friend of Geo Stelar. She EM Wave Changes with the FM-ian Lyra to create Harp Note.
Sonia Strumm is an assumable 11 or 12 years old. In the games, she was a pop singer until she met Geo Stelar, when she rebelled against her manager and retired (only temporarily). In the anime, however, she just wants to sing songs that she wrote herself instead of those written for her. In the midst of these two events, she encounters Lyra. She has a crush on Geo, but like most other females in the games, has not outright admitted it, but strongly pushes it to the audience, this can proven a few times in the Star Force game series. In MegaMan Star Force 3, if you chose to save Sonia's bag and not the others in Alohaha, you'll get a scene with Geo and Sonia, Geo talking about how he is scared of the ocean at night then Sonia offers to hold his hand so he isn't (in which he wholeheartedly agrees), then they go on to talk about the times they had together and she thanks Geo for being her first brother and other things. In MegaMan Star Force 2, if you went to Sonia's Personal Page after forming a BrotherBand with her and looked at her Secret Message, it'll say there's this cute boy she likes which the player will automatically assume is Geo.
Sonia "composes songs for her deceased mother in Heaven." She notes that her mother passed away because of a disease that made her critically ill. She notes that her mother was sick in bed a lot for a year. Little is known about Sonia's deceased mother, as she never appeared in flashbacks (except for Sonia's story about her mother on AMAKEN's roof.) Lyra encountered her when she fought with her manager. Together, they unwillingly turned into Harp Note, She is forced to face MegaMan, or Geo Stelar, who helped her during her conflicts with her manager. After becoming an ally to MegaMan, she grew to like Geo. Sonia finally invited Geo to a date in Times Square, where Luna Platz eavesdropped. Then Ophiuca showed up. Luna did an EM Wave change with Ophiuca to become Queen Ophiuca and ruined Geo's and Sonia's date. In MegaMan Star Force 2 on the Air Display boards, Sonia says "When you're tired, give yourself a boost with Soniavita D. I'll always be here cheering for you."(also used in the anime) How she got her Star Carrier is unknown. Also, a possible Auto Brother says in those two months this game takes place in, Sonia's come out of retirement. Like the prequel, Sonia asks Geo out, but instead of going to Time Square, they go to Wilshire Hills. It is here that Sonia admits what made her want to go back into singing, which was her inspiration from Geo's attitude. She recites a quote that Geo said when Mega Man defeats Harp Note in the first game. This was "I know how you feel, and I want to help you." That is also what made Lyra turn over a new leaf.
At Wilshire Hills, they go to a museum. The exhibits are then being stolen by Solo. She and Geo EM Wave Change and try to stop Solo from finishing stealing all of the artifacts. They succeed but then Omega-Xis swallows a OOPArt, Solo's original planned artifact to steal. Later in a fight with Solo, she is trapped in a teleporter and is dropped into an unknown location. She later resurfaces in the Bermuda Maze as Dr. Vega's ally. She got persuaded by Hollow because they said they will not hurt MegaMan anymore. Later, Lady Vega still attacked MegaMan, and Rogue was about to finish MegaMan off, but Harp Note saved MegaMan. Even though she saved him, she still won't come back. Therefore she also cuts their BrotherBand and fought MegaMan. When she loses, she realizes her mistake and helps MegaMan defeat Rogue, and ultimately Hollow himself.
In MegaMan Star Force 3, she is officially allied with the Satella Police and is registered under Project TC - a registry of those who are allowed to legally perform Wave Change - as No. 004. She stars in a drama show and is about to perform her last live concert when she invites Geo and co. to WBG Studios.
When Taurus Fire attacks during the filming, Geo transforms to MegaMan and defeats Taurus. At that time, the director decided to have MegaMan co-star, instead of Belle, her assistant. Belle's Wizard, Ice, was not happy that Belle lost her role, and gets corrupted by a Noise card to transform into Diamond Ice. Diamond Ice attacked and froze multiple objects at the Studio to prevent Sonia from performing. Eventually, MegaMan defeats Diamond Ice and saves Sonia's performance.
At Alohaha it is revealed that Sonia really loves eating BBQ. Not only that, but during that event, it was also revealed that she could swim. If the player chooses to save Sonia's bag, a scene plays out in which both Geo and Sonia show signs of liking each other. Like her "Summer Vacation" wallpaper, her swimsuit is nearly identical to how she's pictured in that event. In the anime, it was also revealed that she partook in something called the "Popstar Charity Swimming Contest," which she apparently won. Her swimsuit she wore there must've embarrassed her, because when her manager showed it to her, she freaked out about not being able to wear it. The reason for this is unknown, but there is fan speculation that after she came home from it, the kids laughed at her. She then vowed she would never be seen in that again. Sonia also assists MegaMan in his quest while he combats the Dealers, often traveling with him and members of WAZA throughout the second half of the game.