Now back to Kuzan. After Sengoku stepped down, Aokiji was his choice but he was forced to fight Akainu for the Fleet Admiral position.
I believe Aokiji used his final days as Admiral leading upto his fight agaisnt Akainu to visit Mary Geoise and ultimately take a copy of the final Road Ponygliph Or he visited Mary Geoise to meet the Gorosei so he could discuss his retirement and used that opportunity to take a copy of the Poneglyph.
The Marine higher ups has access to Mary Geoise so an Admiral visiting wouldn’t alert them to take higher security measures. No one would even suspect anything if they see a Admiral wandering around especially Aokiji.
Losing Faith in the World Government
There’s plenty you can do without belonging to the Marines. I’m starting to see certain things exactly because I’m not with them anymore
Aokiji wasn’t the only one who lost faith in the World Government. Even Sengoku started to lose faith but stayed with the Government. Aokiji was the only one to act on it and do something about it and stealing that copy which is the last piece to find One Piece, which according to Whitebeard’s final words
Will Turn the World upside down and engulf a Great Battle
This would lead the Downfall of the World Government and the Celestial Dragons.
Who will Kuzan give the copy to?
Nico Robin is the only one who is able to decipher it and Aokiji told her to stay with the Straw Hats and at this point Robin is the only one he could ever trust.
Apparently, one of the reasons that he let Robin go during the destruction of Ohara is because of Saul. He states that he respected Saul’s will and felt it was his duty to watch over Robin’s life until she found her place.
Maybe Aokiji intends to not only allow Nico Robin to fulfill Saul’s last wish but also Ohara’s dream to find out the world history by giving her the final piece to find Laugh Tale.
*Theory by King of Beasts Kaido