The short answer
If you are starting now, there is not really a choice to make: Koikatsu Sunshine can no longer be bought.
The only one still on sale is Koikatsu, as Koikatsu Party on Steam.
Mods are not compatible between them
Despite the similar names, these are separate games. The author of HF Patch notes that Sunshine shares many parts with Koikatsu but is not directly cross-compatible in most cases.
That is why each game has its own all-in-one patch: HF Patch for Koikatsu, and KKS-HF Patch for Sunshine. You cannot use one on the other.
How many mods each one gets
Counting this site's catalogue by supported game:
| Supported game | Entries |
|---|---|
| Koikatsu / Party only | 32 |
| All titles | 32 |
| Koikatsu Sunshine only | 10 |
"All titles" works on either game, so in practice 64 entries apply to Koikatsu and 42 to Sunshine.
Counted while the catalogue holds 74 entries. The numbers move as the catalogue grows.
If you already own Sunshine
KKS-HF Patch is the usual starting point. In the catalogue you can filter by game to see the Sunshine entries.
One more note
The KKS-HF Patch documentation also states that the game can no longer be bought online. This site does not point to unofficial sources.
Last checked: 2026-08-05 (counted while the catalogue holds 74 entries)