How to get key
Gatari is a private server for osu! The access to gatari is invite-based. To create an account on gatari one needs a key.
You can either receive such a key from a friend who plays on gatari (every active player receives a key for a friend once a time period) or purchase it with a monthly supporter.
For ~2.5$ you get a key and premium-status for a month, so the key is technically free in that offer. In order to purchase the key with supporter go to support page and make a payment after filling in your email address instead of username.
After successful payment you will receive the key by email. The payment confirmation can take some time (up to half an hour) so please be patient. If you have any further questions you can get help either in gatari vk group chat or by PM Firedigger.
Respected members of osu! community such as content creators, mapper or top players can contract admins in order to receive a personal invitation.
If you are a strong offline player looking for a server, you can apply for an access to the server with a liveplay proving your skill. Here, "strong" means top 50 gatari material at the time of applying or some kind of unique skill only 10 people in the world can contest. Requirements for the liveplay are explained in FAQ in the section about "Verified legit player" mark.