You require at least 10 partymember for the splitting scene on the 4th floor of map no. 11.
Obtained when going to the left bottom corner in the 4th floor of map no. 12 with less than 10 partymember. If you have the needed amount of 10 partymember, the quest is skipped.
Return with at least 10 party member.
You will also get 1 Earring in a treasure box, a Talisman based on who you bring with you, and some relationship points:
Tsubaki: AIM; +10% hit rate
Trey: Protection; -10% enemy Phy damage
Mira: Healing; +10 recieved healing
Vampire: Magic; +10% mag damage
Mire: Speed; +10% agi
Sandra: Nothing, She even takes the Earring.
Brad: Speed; +10% agi
Chiyo: Magic; +10% mag damage
Elly: Aim; +10% hit rate
Ryoko: Greed; +5% crit rate
Kayelinth: Fire; +10% Phy damage