As with basically every other visual novel Sekai Project launches onto Kickstarter, the campaign for The Grisaia Trilogy was a huge success (barring a few gaffes, of course). In the end they raised money not only for the three main games, but also the Idol Magical Girl Chiru Chiru Michiru spin-off.
Told in an episodic format, Idol Magical Girl Chiru Chiru Michiru focuses on Michiru and all that she gets up to. Please note that there are 13 “episodes” in all, and non-backers will need to pick up both Part 1 (which includes episodes 1-7) and Part 2 (which contains episodes 8-13) on Steam to play through the entire episodic visual novel.
Both Idol Magical Girl Chiru Chiru Michiru Part 1 and Part 2 are available for a currently discounted price of $14.99 each and run exclusively on Windows. This discount ends on August 5, at which point they’ll ramp up to $20 each. If you’re not interested in spin-off shenanigans, then you can instead just play The Fruit of Grisaia proper.