Please note: all credit goes to anima132000!
Guide to Make Lenne Busted
Equipment wise you’ll want Magic Poleyns as an accessory but Bracelet of Magic is also a good candidate if you don’t want to gamble on crit. But Lenne does have a good 15% baseline crit which makes her a good candidate. Class emblem wise you’ll want Pyromancer as your end game.
Passive skills Character passives for me would be TP Up, TP Sacrifice, and Mag Up. If you’re playing a harder difficulty and Lenne is more vulnerable I would honestly switch TP sacrifice for clothes bonus. As for class passives I’d go with Agi Up and Crit Up.
You just have to spam Elemental pact -> Third Eye and proceed to use the corresponding elemental weakness on the enemy since she benefits big time from the modifiers of her two skills. As for attack Heavenly Tear since this will allow Lenne to hit all elemental weaknesses.
That said, you’ll want Glenn around as a member to transfer TP to her along with using All Break to better maximize her output, you can also slot him with a guard skill so he can potentially take hits for her. Glenn can also use Oil Slash to force a fire weakness on an enemy if they don’t carry any elemental weakness.
Viktor is always a staple with Heroic Hymn -> Poetic Ode so as to maximize damage output, he can also provide TP regen to help recover the lost TP from Elemental Pact.
4th member is a toss up but Mikah is a good choice for buffing agility and Sienne for buffing crit chances if you opted for Magic Poleyns.
At that point just keep spamming Third Eye -> Heavenly Tear. You’ll normally be able to take down even the stronger foes by the time your Third Eye runs out. But yeah bear in mind this is a fairly slow output but you can easily hit 10-20K+ in terms of damage late game.