Formerly a prosperous fishing town, the Coral Ward dwindled in prosperity as more and more toxins were emptied into the water, eventually leaving it a near-ghost town. The water is so polluted that most Pokémon can't even touch it.
On the northernmost dock of the town is a mysterious woman mulling over how to rescue an Popplio stranded in the toxic water. Cain shows up and introduces the player to the woman, named Amaria, and takes it upon himself to rescue the Popplio with his Grimer, battling the player to help soothe its jitters.
After obtaining the HMs Surf and Dive, the player can obtain the Coral Key (and an Electirizer as a bonus) hidden in a secret room reached by using dive behind the southern lighthouse (view picture below). The key unlocks the door to the northern lighthouse nearby. Using dive within the northern lighthouse leads the player to an encounter with a Popplio being harassed by a Huntail and Gorebyss. Defeat the two Pokemon to collect Popplio, as well as the nearby TM68 Giga Impact.
This is a main story quest. It will start once You ,Victoria, Arc, and Adrienn escape the Devon Corp facility. Adrienn will ask for volunteers for his gym. However, this quest will give some bonuses if number of volunteers exceed 10.
There's 15 max volunteers. the volunteers include:
Girl near Obsidia park, hug the wall on the right and you'll see her
Slacker hanging out near the bottom entrance of the Slums, yellow hair
Bored guy in Onyx Arcade.
A girl inside an alley directly south when you enter Obsidia from Opal.
Insufferable guy going on about his genius or whatever in front of the Grand Stairway, blue hair
Old lady in Lapis Ward, grey hair, standing in one of the spots with greenery and stuff
A guy near the train station, slightly to the east.
Girl in an alley in the Lower Peridot ward.
On the house with the sick Kricketot, it's a guy with a blue cap. (The first building, out of the underground railnet)
Homeless man in the Blacksteam Shelter in Peridot Ward, he's sitting on a bench somewhere in there
Girl with social anxiety in Jasper Ward (First building to the left, entering by the Peridot Ward)
Kid in Beryl library, pink hair (may need to fight a kecleon in front of the door first if you haven't dealt with the lot of hem yet)
A bug catcher in the north of Beryl.
People watcher girl on top of the wall between Reborn City and The Desert. (place where Corey released his pokemon)
To confirm you got all the 15 volunteers, Adrienn will give you an Ability Capsule and a Star Piece, along with the Wise Glasses.
Slightly increases your favor with Adrienn when exceeding 10
Wise Glasses 10+
Ability Capsule, Star Piece
Note: just remember that the volunteers are all within the city walls. You're not gonna find someone in Spinel town randomly deciding to volunteer for something in Reborn City. And that some items COULD be replaced when going up the number of volunteers.
In the house to the left of the Pokémon Center, a young boy frets over a Skitty that has taken a rough fall. He's certain he can help it himself, even without the Pokémon Center, but his grandmother knows he needs something like an Ultra Potion to help. If the player has one in their bag, they can give it to the boy and let him heal Skitty himself. He still worries about what would happen if he just let it go out into the wild again, so, exasperated, his grandmother asks if the player would be willing to look after it for them. The Skitty will know one of these moves: Wish, Sucker Punch or Zen Headbutt.
After obtaining the Warehouse Key from the Obsidia Ward, the lower storage unit by the docks can be opened, revealing the true Day Care Couple. They give the player their heartfelt thanks and tell them they are welcome at their Day Care any time.
The Warehouse Key also unlocks the storage unit south of the Pokémon Center. After the Day Care Couple have been released, a Team Meteor Grunt will appear, counting up the Pokémon stolen from the Day Care. The Grunt notices the player and complains about their constant interference, but chooses to escape rather than confront the player, their task completed. With the Grunt gone, the player can make their way to the back of the storage unit, where a lost Happiny has ended up.