I don't know now, but for the longest time, Google made a much better Japanese IME for Windows than Microsoft ("Google Japanese Input"). I started using it when running into reliability issues, like disappearing kanji dictionary, or frozen switching between roman and hiragana.

Assuming Microsoft's Japanese IME is still a dumpster fire, and the Google one has not succumbed to Googleshitification, that would be a way to go.

To enable the Microsoft IME there are some rituals to go through like adding the Japanese language and then a Japanese keyboard under that. It will download some materials, like fonts and dictionaries. A reboot is typically not required, I think, unless you make Japanese the primary language.

Once you have the keyboard, LeftShift + LeftAlt chord goes among the input methods. Ctrl + CapsLock toggles hiragana/romaji input. I think these are the same for Google or MS input.