The official Pokémon movie website has updated. Translations follow:

Rica Matsumoto and Asuca Hayashi Make A Surprise Appearance at the "Pikachu Outbreak-chu!"!

Rica Matsumoto and Asuca Hayashi made a surprise appearance on Thursday August 10th at the Super Soaking Splash Show "Water Carnival" during the "Not-Just-Pikachu Pikachu Outbreak-chu" being held in the Yokohama Minato Mirai area.
They had come to sing the opening theme song and the ending theme song to "Pocket Monsters the Movie: I Choose You!"



There was already a huge crowd gathered around the stage set up at the Red Brick Warehouse, since the "Water Carnival" show was about to begin there.
The "Water Carnival" involves Pikachu dancing lightly along to Latin rhythms!
The audience got super soaked by the water fired from the water cannons! Everyone were in a great mood!
(The Super Soaking Splash Show "Water Carnival" is held until Tuesday August 15th)

After the "Water Carnival" ended, the audience prepared to leave, but then they suddenly heard Satoshi's voice?!
To everyone's surprise, Satoshi voice actor Rica Matsumoto appeared on stage!
The people that had started leaving spot her and make their way back to the stage as well.



Matsumoto performed "Mezase Pokémon Master -20th Anniversary-" to great cheers from the audience.
And of course, the audience started singing along as well! The audience's chorus during the music interlude isn't something anyone will forget either.
After the song was done, Matsumoto commented "I've been wanting to sing a singalong song that connects everyone from children to the elderly.
When I was told I was going to sing "MezaPoké" again, I thought "All right!""



Next, Asuca Hayashi appeared on the stage as well, to everyone's surprise!
Hayashi also did the ending theme song to "The Seven-Day Wishing Star Jirachi" 14 years ago.
When the moderator asked the audience "Did anyone here watch "The Seven-Day Wishing Star Jirachi?", lots of people raised their hands.
Hayashi then went on to perform "Chiisaki Mono" and "Oración: Let's Walk Together".
The venue got filled with a calm and mellow atmosphere.

At the end, everyone that had come to the Red Brick Warehouse took a memorial photo together, where they struck the "I Choose You!" pose!



Source: http://www.pokemon-movie.jp/news/?p=3114