Yesterday I was messing around with increasing damage. My damage record is 126 billion.The battle used here was 'Dinner' Time! , the third 7 World Redux battle. Damage gets multiplied the higher the hit counter is.
To get a high hit count, it involves prolonging the Fever Time mechanic as long as possible by captivating a small crystal right before Fever Time runs out. It only lasts 10 turns, so after doing 9 Fever Hits, capivate another Small Crystal.
Syrma was only level 1 in video in order for the "Magic Lightning Conditional" to activate.
See Conditional skills list (Mugen Souls Z) to see to get them.
Magic Lightning - 50% extra magic attack if enemy higher level
Boss Presence - 100% extra magic and physical damage if enemy is at 100% HP remaining
Resuscitation - 20% Special Attack boost
Syrma Equipment (all level 999):
Spear Skill Master+150
Critical Rate Up+100
Magic Damage Up+50
Overwhelming Aura Belt
Sun Goddess Medal
Ultimate Peon's Collar
Magic Enhance from Coffin Effect
INT - 26,200,183
MND - 48,564,289
AGI - 34,038,216
TEC - 34,038,222
MOVE - 1,000