There are a total of seven extra Achievements/Trophies which are a part of the Assassin’s Creed Unity: Dead King DLC. Defender of Franciade is one of these Achievements/Trophies.
How to get Defender of Franciade Achievement/Trophy:
To get the Defender of Franciade you need to solve the 7 Suger’s Legacy Riddles in this DLC. By completing all the 7 Suger’s Legacy Riddles you will unlock a very powerful sword called Eagle of Suger.
If you have played the main game Assassin’s Creed Unity, yo might be aware of the Nostradamus Enigmas. If you have solved them, Suger’s Legacy Riddles will be like a piece of cake for you.
You need to look for hidden symbols in the town of Franciade. You will easily solve the first two Suger Legacy quests as the are a part of the main story. They take place after completing Sequence 13, Memory 3 and unlock the starting points of the other 5 quests on your world map.
To play the DLC and access the town of Franciade you have to use the carriage near the Café Théâtre in Paris. Watch the following video for extra information: