Here is Pokemon Fan's coverage of what details we have on the movie so far:
http://i.imgur.com/obJWy01.jpg
A special report on the start of Satoshi and Pikachu's journey!
We've finally got a glimpse of the movie's story! We'll also present the newly discovered Pokémon and the travel companions in detail!!
Setting off with Houou as the goal!
The "Rainbow Feather" Houou gave Satoshi serves as their guide for the journey!!
http://i.imgur.com/oEtj5gU.jpg
From completely incompatible to true partners!
After meeting Pikachu, Satoshi finally sets off on his journey! What kind of adventure awaits him on his journey in search of Houou?
"I like you!"
Satoshi and Pikachu's meeting!
Satoshi also started out as a rookie Pokémon Trainer. But even though Pikachu won't listen to him, he gets through to it little by little.
"Let's go meet it!"
The start of the adventure!!
They witness Houou, which flaps its beautiful wings as it flies through the sky! Meeting this legendary Pokémon again then becomes the duo's goal!
Encounters with travelmates!
As the journey continues on, companions that will travel with Satoshi appear! Both the humans and the Pokémon are irreplaceable friends!
Makoto and Soji, Pokémon Trainers: They will teach Satoshi lots of things he doesn't know.
Butterfree and Hitokage, Pokémon: Together with the Pokémon he befriends, Satoshi heads for his next encounter!
A tough opponent that stands in his way: Cross!
When Trainers meet, they have a Pokémon battle! Some opponents focus purely on physical strength to win!
http://i.imgur.com/eKYEUUy.jpg
Friends! Pokémon! New encounters!!
These are the people and Pokémon Satoshi meets on his journey. It's confirmed that a newly discovered Pokémon will be among them!!
Trainers! Pokémon! All kinds of encounter lie in wait!!
Companions, a rival and a person that helps Satoshi! For the first time ever, the journey is truly overflowing with such encounter! And in the movie, a Pokémon nobody yet knew of , one resembling a black shadow, will appear! And so will a certain Pokémon from the Alola region!
Marshadow:
It hid in Satoshi's shadow without anyone noticing. Is it actually Marshadow that's been guiding Satoshi as well?!
(A Pokémon quietly appeared from Satoshi's shadow!)
Cross:
A Trainer that travels with a Gaogaen. He believes that strength is everything.
Gaogaen:
In addition to moves that shoot out fire, it also specializes in punching and kicking!
Pochama:
Makoto's partner. It gets carried away rather easily.
Lucario:
Soji's partner. It has the power to read others' emotions.
Lizardon:
Does Satoshi meet this Pokémon somewhere on his journey...?
Soji:
He knows extremely much about Pokémon, and his goal is to eventually become a Pokémon Professor.
Makoto:
An energetic girl Trainer that's Satoshi's equal!
Joy:
She will treat injured Pokémon at the Pokémon Center.
Bonji:
A researcher that has chased after Houou for a long time.