This maintenance droid is the most zealous of the Goddess' protectors, so she will descend whenever anything threatens her or the structural integrity of Sol Marta. Therefore, she is a recurrent and strong enemy the player will fight at multiple points during the game's story.
1st Battle
This battle also doubles as a tutorial for the Replekia and Super Move mechanics, so it isn't very hard. However, the player shouldn't drop their guard, as getting killed in this battle without using a Song Magic charged with Replekia is a Game Over. Still, it shouldn't be pretty difficult to do this, as using Harmonics attacks the first two Attack Phases should be enough to use Replekia, and having the full IPD chorus (100) as a free demonstration of sorts of its power, coupled with the low MP both Luca and Cloche should have at this point in the game, it should be pretty easy to mop the floor with the enemies accompanying ???, who herself won't take any actions in this battle until the player has used Replekia.
However, once they have done this, she will announce that Replekia doesn't compare to her true power, which will be followed by using the X: Side Slicer attack, which hits all party members once for massive damage. If the player doesn't block this attack with a Perfect, the damage sustained will kill their party instantly, and in fact, it would be better for the player to let themselves get killed by it. They can continue blocking the attacks if they want, but it will be pointless because ???'s HP can't be reduced beyond 1, so this is a battle they must lose to continue with the game. However, it could be interesting for them to use this occasion to preview ???'s other attacks, if they can survive long enough to see them all: Vesper hits all party members six times for large damage, Minute's Knock is single hit to a party member that deals average damage that can be hard to see coming due to its speed; Combination, which hits a party member six times; and Delay Attack is a single hit to a party member that causes Stun.
2nd Battle
In this battle, Raki isn't very different from how she was in the first one after having used Replekia, so the player will have to stay on their toes in order to block all of her incoming attacks, which can easily down the party if they aren't careful, so it's advised to first begin with Blue Magic and then convert it into Red Magic after the party has been healed enough. The most advisable way of action to defeat her would be using either Jakuri/Luca and Cloche (depending on the route) and launch a Replekia-charged Song Magic to defeat Raki quickly. However, if the player chooses to fight without Replekia due to not wanting to use it or because of not having Cloche in their active party, they will have to depend purely on the strongest songs they have at that point (all of which depend on the route the player is going through) and on the Super Moves of the Vanguards.
3rd Battle
The final compulsory battle against Raki isn't very different from the previous ones, so the strategy for battling her is pretty much the same as the one for the second battle. However, it must be noted that for those playing the American version, this is the infamously bugged battle: in this battle, Raki gains a new skill called Fractal Change, which should activate a random Jamming effect and shift her stats and AI patterns between five different profiles every time it gets applied, but due to the fact that the skill's complete code block was zeroed out; the game ends up crashing and freezing whenever Raki tries to use the skill. She will always use this skill on the third Defense Phase of the battle, so the players will have to do their best to defeat her before this happens, or at least deal more than 60,000 damage to her; in which case Raki will use X:Side Slicer instead and leave Fractal Change for her next turn. Luckily, the Vanguards should be of a high enough level, the Reyvateils should have acquired by now their respective ultimate songs (unless the player is going for Cocona's ending), and the player should have amassed at least more than half of the max IPD chorus for Replekia, so defeating Raki in such a short time shouldn't be much problem.
As for the JP and EU version players, they don't have to worry about the bug, so they can fight normally. However, it must be added that depending on the Reyvateils for this battle could be rather dangerous due to the random Jamming, but if their Vanguards are of a high enough level, they shouldn't have no problem with Raki, especially if they have synthesized some attack items and bombs in order to increase their damage output.
Additionally, Raki can be fought as much as the player wants, gaining more power with each battle, although she will stop powering up after the 15th battle and won't change her skillset from the one used for this battle. Likewise, every five battles the player wins, Raki will give them an extra illustration for their Extras menu. However, this will be impossible to fully unlock in the NA version due to the bug unless the player exploits a glitch that extends their Action Time, so unless they can have access to an unofficial fixed version, they should just ignore these extra rewards.