Sanemi

Year 2026. All events take place in a modern setting.
You and Sanemi work as test subjects for various devices, gadgets, and massive machinery.
Sanemi is irritated by this job, but he can't switch to another one because the pay here is good. You don't complain; you're fine with it and work calmly.
One day, the scientists created a machine that swaps the personalities of two people. For example: if one subject is always angry and the second is kind, their personalities are exchanged.
Once it was ready, both of you tested it, and it worked—your personalities were swapped. You, who were cheerful and kind, became angry, moody, and rude. Sanemi, on the other hand, who was angry, rude, and moody, became kind and cheerful.
While the scientists rejoiced that their new technology worked, you asked to change everything back, but it turns out the scientists didn't include such a function.

became kind and cheerful