Hard Reki (Perfect/No Hit)「BlazBlue Entropy Effect」
7Figured I'd upload the run I had with no hit as reference for people wanting to get the achievement for a perfect Reki fight.
Main setup is Black hole Slow, Black hole Durability (Gold (4 seconds)), and (optional) Legacy Recovery up.
You'll want to use the first two skills to get as much damage off; from there, you'll want to hold on the third skill until Reki utilizes one of her three attacks, either her lunge up to drop to lances and then land, the back jump to do a wave across the screen, or the overhead slash combo. After she initiates one of these three, you'll want to use your third and fourth legacy skills to finish her off. You want to do this with such timing so that you can skip her DM attack, as you CANNOT push her to phase 2 until she finishes the attack after her final attack that is unavoidable (you have to crouch, stay away, and then dash in after the lightning waves move out, and then wait a second till her invuln falls off).
For the first part of phase 2, she'll be immune to ALL CC (crowd control) (e.g., slow, freeze, stun, etc.). She can only be punished shortly after each attack. You can break her for small combo after the dash attack, but only if it's not the first one
Her attacks from here break out into four attacks, back up into the corner for triple over head followed by another triple, dash across the screen once, then double dash again (can be punished if not first move), jumping overhead followed up by a wide unavoidable slash, and the final attack that throws her sword like a boomerang that also summons lightning attacks.
After you do nearly half her HP, she'll push into her second part of phase 2. From here, she'll summon a dark clone to do the boomerang throw followed by lightning. She will be come susceptible to CC's again, so NOW is the time to unleash all you have behind her and try to finish her off.
Her moveset from here is slightly slower and basically mirrored. She can do triple waves together with each form, she can dash while the other throws the boomerang with lightning and, finally, she can do the overhead slash followed with the unavoidable while the other dashes (or maybe it was boomerang?). Regardless, it all falls back to her four moves during this phase.
Hopefully this at least gives you a frame of reference you can do as well as the guide above to at least know her moveset.