Bulma would be excited. She might see it as an opportunity to dress Goku up in different outfits and give her a new look. She would also be curious about any changes in Goku's personality. Android 18 might be indifferent at first, but as she sees Goku in action in the new form, she would start to analyze if there are any differences in her combat style. Mr. Satan would probably be completely confused and might think it's some new kind of magic trick that he can't understand.
Krillin would probably be one of the first to be accepting. He's always been Goku's friend and would likely see Goku's inner strength regardless of the physical form. He might even joke about it a bit at first. Vegeta, on the other hand, would be initially shocked and perhaps a bit dismissive. But as he sees Goku's power in the new form, he would gradually come to respect it. Gohan would be very curious and would want to know how this transformation happened and what it means for their future battles.
Sasuke might be extremely suspicious. He has a long - standing relationship with Orochimaru, and this sudden change would make him wonder if it's a new trick. He would keep a close eye on her to see if she's still the same threat.
Haku would likely be very protective. He has a special bond with Chihiro already, so when she turns into a spirit, he would probably try to guide her through the changes. He might teach her how to use her new spiritual powers. No - Face, on the other hand, could be either curious or envious. Since No - Face is always in search of something, seeing Chihiro transform into a spirit might make him wonder if she has found a new kind of fulfillment. The bathhouse workers might be initially shocked and a bit afraid. They are used to dealing with normal spirits, but Chihiro's transformation is something unexpected and they might worry about how it will affect the balance in the bathhouse.
Tails would probably be very curious and eager to figure out how to change Sonic back. He might study Sonic's new form scientifically. Knuckles, on the other hand, would be a bit more confused but still stand by Sonic's side. Amy might be initially jealous because she's used to being the main female around Sonic, but then she could become a great friend and help Sonic adjust. Dr. Eggman would likely see this as an opportunity to take advantage of Sonic's confusion in her new form.
Germany might be really confused at first. He's used to Prussia as his older brother figure, so seeing Prussia as a girl would be a big shock. He might be a bit protective in a different way than before. Italy would probably be very excited and might even start flirting a bit. He's always been a bit of a ladies' man, so he'd be intrigued by this new female Prussia.
Jiraiya would have a very interesting reaction. Since he's a bit of a pervert in the series, he would have to really adjust his behavior. He might also see this as an opportunity to study the differences in chakra and fighting styles between male and female ninjas while also trying to guide Naruto in this new form.
Some characters might be very shocked at first. For example, Sandstorm, if she was in a relationship with Firestar before, would be confused and have to re - evaluate her feelings. But others, like Graystripe, might be more accepting and just see it as another change that they have to adapt to. Younger cats in the clan would probably be more curious and excited about this new Firestar.
Rukia would probably be one of the first to be both shocked and amused. She might tease Ichigo a bit at first but then quickly get serious about helping him. Chad would be very accepting and offer his protection as usual. Uryu might be a bit more skeptical at first, thinking it's some kind of new Hollow trick. Orihime would be very empathetic and try to make Ichigo feel comfortable in his new form, maybe even offer to make some new clothes for him to fit his new body.
The other characters' reactions would be quite diverse. For the more competitive male players, they might see this as an advantage or a disadvantage depending on their relationship with Kirito. If they were rivals, they might think it's a chance to outdo him now that he's a girl. But if they were friends, they would offer support. Female characters like Silica might be excited to have another girl around and might start sharing girl - only things with Kirito. The guild members of Kirito's previous guilds would likely be confused but still accept him, after all, they know it's still Kirito inside.
The other Pokemon in the Pokemon Center where Pikachu is usually treated would be very frightened. Nurse Joy would be at a loss as to what to do, as she has never seen Pikachu act this way. Professor Oak would be extremely concerned and would start researching immediately to find out what could have caused this sudden change in Pikachu. Team Rocket, on the other hand, might initially see this as an opportunity to capture Pikachu more easily, but they would soon realize that an evil Pikachu is far more dangerous than they expected and might end up getting in over their heads.
Sonic might be initially shocked and a bit confused. But being the hero he is, he would probably give her a chance to prove herself. Tails would be very curious and might try to figure out how the transformation happened scientifically. Knuckles would be more guarded, not trusting her right away. Dr. Eggman, on the other hand, could be either furious if it wasn't part of his plan or intrigued if he sees potential in this new form for his evil schemes.