So, for everyone loving this idea and feature (which is fair, it's awesome), please keep the following in mind:
a.gup.pe (which provides the features) is not a part of mastodon, and neither groups as a feature. a.gup.pe are an independent organisation.
And like instance admins and mastodon itself, they rely on donations to pay the bills.
In fact, they have a co-op, which is cool!
See here for how you can join in and support them: https://opencollective.com/guppe-groups
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.