For Athena
Uncommon11.5%ObjectiveOptionalAnywhere
For Athena's Fortune a Legend can sail, an Emissary of those who prevail.
NB Athena's Fortune only becomes accessible once you're a Pirate Legend.
There is no level requirement to buy the flag for Athene's fortune. Then (in the same room/area as the representative) vote to be emissary on the nearby table.
This will unlock if you're in a crew and you only vote - i.e. even if you're under lvl 15 and someone else buys the flag.
Conversely - you can also do this solo; just buy the flag and vote solo to raise it.
NB being an emissary increases XP gains significantly - helping with other achievement grinds.