Champion of Chi-Ji

Earned after completing the following storyline told in a series of quests for The August Celestials at the Cradle of Chi-Ji .

Ellia Ravenmane
Minh Do-Tan
Ellia Ravenmane: Rematch
Fat Long-Fat
Julia Bates
Dextrous Izissha
Kuo-Na Quillpaw
Ellia Ravenmane: Revenge
Tukka-Tuk
Huck Wheelbarrow
Mindel Sunspeaker
Yan Quillpaw
Fat Long-Fat: Rematch
Thelonius
Ellia Ravenmane: Redemption

Just to add a little extra to this. You'll get one of these quests each time you get the August Celestial Dailies at the Cradle of Chi-Ji. Once you've defeated ten students, collected three spirits and ten feathers, you'll be given one of these quests.

They appear to be successive and follow the order in Calesta's post above. You don't appear to get repeats. Definitely worth noting that if you're on a day when you don't get Chi-Ji dailies then you wont get to fight the next combatant. It would take a minimum of 15 days to complete this achievement but as the August Celestial Dailies are at a random temple each day, expect this to take longer with other temples interspersed.

It is unclear if there is a reptuation requirement but it would seem that there isn't.
Speculatively, if there is, it would impact whether or not you get Chi-Ji dailies or a different temple on a given day.
e.g. You might not get Chi-Ji dailies for the final Ella Ravenmane quest until revered.

you need REVERED with GOLDEN LOTUS to unlock the quests