To achieve the maximum rating in the game, understanding how calculations are made is crucial. The rating system appears to be based on both accuracy, grade, and difficulty of the song, with the game taking into account the top 21 accuracy scores for these calculations.

As such, it is important to maximise the amount of songs that you purchase that include EX 9 charts, while also minimising spending.

Given the importance of purchasing songs with EX 9 charts, I shall be sharing the full list of them. Below are the required purchases to achieve a perfect rating score on Starri:

Slash Charts (EX 9):
- Don't Worry Baby (Starri Originals Vol.1)
- Extraordinary (Full Steam Ahead)
- SIGMA* (Regular Pass, Level 25)
- Rapsodie fer za Cactuses (Starri Pass, Level 23)
- Bandit (Regular Pass, Level 23)
- Night Theat+er Etude (Regular Pass, Level 18)
- Brain Power (Regular Pass, Level 15)
- MiLK (Starri Pass, Level 12)

Catch Charts (EX 9)
- Intuition (Full Steam Ahead)
- The Best Christmas Ever (A Merry Merry Mix)
- c.s.q.n. (Indie Favorites)
- Conflict (Indie Favorites)
- SIGMA (Full Steam Ahead)
- Rapsodie fer za Cactuses (Starri Pass, Level 23)
- Night Theat+er Etude (Regular Pass, Level 18)
- Brain Power (Regular Pass, Level 15)

To access the required charts, the following purchases are necessary:
- Starri Pass (comes with the Steam version of the game, mandatory real-world currency purchase)
- Indie Favorites (included with 3000 KCAL Music Marathon)
- A Merry Merry Mix (included with 3000 KCAL Music Marathon)
- Full Steam Ahead
- Starri Originals Vol.1

However, as of the time of writing, A Merry Merry Mix is not available for individual purchase. It is, however, included in the 3000 KCAL Music Marathon, which also covers Indie Favorites.

The optimal purchase strategy would likely involve acquiring the Starri Pass, 3000 KCAL Music Marathon, Full Steam Ahead, and Starri Originals Vol.1. Note that 3000 KCAL Music Marathon may be substituted with Indie Favorites and A Merry Merry Mix, depending on availability and player preference.

Two purchasing strategies can be identified for reaching the maximum rating score.

Option 1: Purchase the 3000 KCAL Music Marathon
This option is currently the one which costs the most.
- The Starri Steam application sits at $19.99 USD.
- The 3000 KCAL Music Marathon package sits at $44.99 USD.
- Full Steam Ahead sits at 299 Gems.
- Starri Originals Vol. 1 sits at 299 Gems.

In summation, one would need to spend $64.98 USD and 598 Gems with this method. The 598 Gems can be converted to $11.48 USD using the $47.99/2500 ratio of the Best Value purchase for gems.

Option 2: Wait for the A Merry Merry Mix Song Pack
This option is currently the one which costs the least, but would require one to wait until A Merry Merry Mix song pack availability.
- The Starri Steam application sits at $19.99 USD.
- Indie Favorites sits at 299 Gems
- A Merry Merry Mix was traditionally at 199 Gems.
- Full Steam Ahead sits at 299 Gems.
- Starri Originals Vol. 1 sits at 299 Gems.

In summation, one would need to spend $19.99 USD and 1096 Gems with this method. The 598 Gems can be converted to $21.04 USD using the $47.99/2500 ratio of the Best Value purchase for gems.

Before I conclude this post, I would like to discuss the Gem economy of this game. It may have been noticed that in my previous section, I did not sum up the Gem to USD values. This is because gems are fairly accessible with consistent exercise.

For example, in order to get 1096 Gems, it would take only 274 days of consistent exercise. This is more than accessible, given that Nex Team Inc. has slowed down progression of the Starri Steam/Mobile versions in favour of their entertainment system[playground.nex.inc], which notably has more songs that have yet to be released to the Steam/Mobile players.

In conclusion, maximise the amount of songs you purchase with EX 9 charts. The list is detailed in the sections above. I hope this helps everyone and happy exercising & spending :)