Rename "master" branch to "senpai" (literal copy/paste of https://stackoverflow.com/a/8762634/11894221 , please upvote that man if you can)

masterToSenpai.sh

git checkout master # Checkout your master branch,
git branch senpai # create your senpai branch ,
git checkout senpai # switch to it,
git push origin senpai # push that to the server.

# Now go on GitHub/Atlassian/GUI to change default branch from master to senpai. Afaik it cant be done via CLI. Then,

git push origin :master # Delete the master branch reference on the server,
git branch -d master # delete the local master branch

# Bonus: set git alias so you can 'git notice-me senpai'

git config --global alias.notice-me 'push origin'