Ar tonelico II: Melody of Metafalica

at least your Vanguard must have high ATK and YOur Reyvateils charged up with Strong Song Magic(and i suggest you to use Replakia ) and shoot it before the Third turn.

if you can't defeat it too.you must increase your Vanguard Level.

Agree, you vanguard and you reyveteils must be strong enough to defeat raki in 2 turn. For me, i use cloche (replakia) and jacqli (my slave 'cause her magic is the strongest after all)

Don't forget to use the equipable IPDs skills to your advantage

I used replakia and super potential coz it's my most powerful magic and use overtuner to synch your reyvateil in an instant on your second turn..
i charged over 772000% and did 68000 damage to her.
of course your vanguard must have decent attack.
i suggest croix and leglius equipped with girl power that increase base damage +++ and action time +++

Have high damage item.
sorry for my bad english

Synthesize bombs like Ar Tolineco and Ar Toluneco(sp?) if you can. Most of Jacqli's bombs do rather high damage, so use them to eke out more damage when you aren't busy upping your emotion gauges. With your vanguard members at around 55-60 (which is about what you should be if you haven't run from any fights...), just your vanguard's EX attacks should put her at close to dead or well beyond it, assuming you've done the synthesis events and have your best synthesizeable gear. EX attacks can be achieved on the third turn rather easily, and Replakia can be started on the second turn (with a little luck, start it as soon as you can). Between the EX attacks you pull out on third turn and most Replakia'D songs (and any high damage bombs you throw at her), killing Raki is no problem. Alternatively, you could just use the Song Recast glitch, although you may consider that to be cheating (although if you're curious, look it up on Youtube).