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The fifth and final case ofPhoenix Wright: Ace Attorney Dual Destinies(not including the special case that involves a truly bizarre case in which you defend an orca) carries on directly after the previous case in the game. This case is the climax of Dual Destinies, directly dealing with the pasts of Athena and Simon Blackquill, and how they can work to dispel this dark age of law.
As ever, this walkthrough will be as spoiler-free as possible, only providing the actions you need to take both in the investigation portions of the episode and the trial sections.

Investigation
Playing as Phoenix, you’ll begin this episode at the Wright Anything Agency with Trucy. Talk to her if you want to, and thenMove to the Cosmos Space Center Entranceto spot Cosmos - follow him then to theBoarding LoungeandTalk to Starbuckabout everything - you’ll end up prompted to examine the museum corridor -Examine the leaves to the left and the fingerprint machine on the right.
Move back to theEntrance,and you’re able to finallyTalk to Cosmos. Doing so, however, will reveal somePsyche Locks. Present the Magatama to tackle them:

After breaking the locks,Talkto him about everything. After finishing,Move to the Museum and Talk to Juniper there. To finish speaking with her,Present her with the HAT-1 Exhibit. You’ll automatically head to the Detention Center and speak to Fulbright and Tonate.
Once you regain control, Move to the Robotics Lab.Talk to Aura about everythinghere, and you’ll be moved to the Entrance automatically. Move to the Wright Anything Agency and you’ll meet up withPearl-Talkto her about everything. With that, you can nowMove to the Detention CentertoTalk with Blackquill and Fulbright.

Watch the scenes that follow, Talking about everything when prompted. When confronted with a choice, choose ‘Retry it in court’ to progress. You’ll eventually find yourself back in theRobotics Lab.
Talk to Edgeworthabout everything and thenExamine the following:

After examining all you need to,Edgeworth will talk to you. Finish Talking to him and then do the same withAthenaback at the Detention Center.
Present Athena with the Robots with a Heartbinder and thenTalkto her about the past. With that, you’ll move on to the final trial of the game.

Cross-Examination: What I Saw
Cross-Examination: Seven Years Ago
This is functionally the end of any cross-examinations for now, but there’s still the matter of Athena’s innocence to deal with.
Proving Athena Innocent
After this sequence of events, there will be a break before the final sequence of testimonies.
Cross-Examination: The Embodiment Of Justice
Cross-Examination: My Fear Of The Moon Rock
Congratulations, that’s the end of Dual Destinies! From here, you’re able to proceed to the optional special case or move on to Spirit of Justice!
