Finding a branch point with Git?

[Note: apologies for using the historically-default name "master" -- I'd change it to "main", but that would break the shas of the example repo.] I was looking for the same thing, and I found this question. Thank you for asking it! However, I found that the answers I see here don't seem to quite give the answer you asked for (or that I was looking for) -- they seem to give the G commit, instead of

[warufuzaketaichi]

git merge-base