[FairyKing]

It would depend on the theme of the form items, and whether it was for a hero, anti-hero or villain rider. But there's three voices I'd really like to hear from henshin devices:

For a tech-based Rider, a cool feminine robotic voice, with a calm tone but not entirely emotionless, and lines that sound like she's giving snarky advice. Basically like GLaDOS.

For a magic-based Rider, an energetic voice, but instead of high-pitched like the Gamer and Build drivers, it should be deep and booming with lots of chanting.

And for a mysterious Rider, a voice that's hoarse and raspy to sound like a whisper (despite being at a normal volume) and with phrases that are short and to the point.