Step 1: access the control panel in the courageous 2 and view all three side objectives ( The Alster harvest festival, Saving officer Alan, Einhel keep monster) The location of each objective is specified in the quest tab. To speed the harvest mission up: Sunny lillies can be found on Bryonia Island (there'll be a green !), Gallet flour can be purchased at the P&R company, and lastly the herb can be found in the branch campus garden.

Step 2 will require you to find 3 spread out side objectives and beat the optional 5 bosses to collect their lost arts
The first mission is called " showdown of the decade" This mission is found on the deck of the courageous 2 and you'll have to play a match of vantage against crow to complete this mission.

The remaining missions are called "ghosts of hamel and missing persons report"
It'll come to no surprise that you can find the ghosts mission at the entrance of Hamel city. To start this mission you will need to bring Ash and Tito with you.
Missing person report will be found at Diana's store in Milsante - you will have to take Juna and randy with you on this quest.

Lost arts locations :
Frozen Epoch
obtained from 8/9 from Fornelius (level 100) at the entrance to the Magical Forest

Leanan's Kiss
obtained from 8/20 from the Magic Knight Regulus-Zamiel (level 111) on Bryonia Island

Prominence Nova
obtained from 8/22 from Agaragion (Lv. 122) in the Osgiliath Basin

Grail Thelas
obtained from 8/27 from Jilvaglyph (level 133) on Auros Coastal Road 1

Aeonian Emperor
obtained on 9/1 from Loa Phantasma (level 144) on the roof of Stargazer's Tower

You will then be called on the Arcuss 2 to start the quest "???". This quest is located on Auros coastal road.

These missions need to be completed before starting the final dungeon.

You can access a portal at the final dungeon in a completed save which will let you get to the true ending.