Daitama
You’ll receive a new topic. Read it from the Gamepad. You may need to select your responses and tap on the screen to view the entire conversation. Go around the path to the right to reach Tsubasa. Talk to her. After the conversation, follow her inside the stage area to trigger a cutscene. After the scene, touch the gate to enter Illusionary Daitama.
Illusionary Daitama, Upper Level
Follow the path and read the message you’ll receive from Touma. You can use the map in the Gamepad for Navigation. Next, continue to the elevator to reach the lower level.
Illusionary Daitama, Lower Level
Continue forth to trigger a cutscene. You’ll be forced off the ledge by one of the hooded ghostly figures so you’ll have no choice but to enter the door ahead. Examine the door and opt to proceed and trigger a cutscene. Shortly after that, you’ll be thrown in a battle in your Carnage Form.
All the enemies are weak against Zio, Itsuki’s Mirage skill so use that consistently in the battle. Tsubasa’s skill is healing so you can have her perform ordinary attacks for now. After the battle and when you resume control, you can save the game and check out the new options in the menu. Leave the observatory afterward.
Shortly after walking ahead, an enemy Mirage will appear. The game recommends knocking down the mirage with your sword attack then engaging it to start an advantage in combat. This basically what you need to do when you encounter enemy mirages when you're exploring other dungeons/ idolaspheres. Do that the enemy ahead and defeat it. After the battle, you should be able to increase your current Carnage Form’s mastery and learn new skills from Chrom and Caeda.
The floating diamond thingies are item containers. Touch them to receive the items inside. The nearest one in your position contains Medicine x2. An enemy may appear from your starting point. You can engage it in battle to get a tutorial about Sessions.
Continue forth to encounter two enemy mirage. Engage them then collect the Revival Bead x2 from the nearby item container. Proceed and ignore the wall for the meantime then take the lift ahead.
Illusionary Daitama, Upper Level
Shortly after moving from the lift, you’ll get another message from Touma. Read his message and you’ll be thrown in another battle afterward. If you defeated all enemies from the previous floor, Tsubasa should have the Skewer skill unlocked. This can be used to trigger a Session with Itsuki and effective against the mage enemies. Use that to take out the mages quickly.
Continue forth and defeat more enemies. Get the Chakra Drop x2 from the item container in the dead-end path nearby. Proceed along the way and pick up First Aid x2 in the NE corner (refer to the Gamepad map)
There are more enemies ahead and you must be running low on EP and health. If you don’t want to use items, you can touch the green light to fully replenish your HP and EP so you can engage more mirage in the area and get additional EXP and rewards. There’s a lift going that leads to several item containers but it is protected by another wall as well. Ignore that for now, ensure you’re healed and save your game then enter the round, red building to face this Idolasphere's boss.
Boss: Gojiun
During the intro cutscene, Touma will arrive, which will bring your combat party to its full members. To start off the battle, target the two Caspars first to prevent the boss from triggering a session in case he hits the weakness of one of your members. Hit the Caspars with Zio to trigger a session with Tsubasa.
If you have Tsubasa's Tarukaja skill unlocked, use that in this battle to get your party's offense up for three rounds. Gojuin is weak against fire so you can use Touma's Fire Strike on him. Unfortunately, since Tsubasa and Itsuki doesn't have the necessary Session skills yet to complement this skill, use Touma's Skewer instead to allow Itsuki and Tsubasa to join the attack with their Session skills. You can use Tsubasa's Skewer as well but that will only allow Itsuki to join the session. Remember to heal whenever needed.
When Gojuin is about to die, he will hide and produce three blob enemies. You need to target the one with the black flame to force Gojuin to appear. Continue attacking him to finish him off.
After the battle, you can go back from where you came from and the enemy mirage will be respawning again. Since there’s a healing point nearby, you can spend a few battles here to farm for exp and other items. Touma has joined your party as well so the battles will be much quicker and easier.
When you’re ready to leave, exit to the left. Jump off the ledge and head to the exit. You’ll be ambushed by several enemies. You’ll have the option to fight or run. Whatever you choose, you’ll be saved by Kiria. More cutscenes will follow. You'll meet Maiko, the current manager of the talent agency called Fortuna. After that, the prologue will end.