In Blade body, use Allegro ender (46%)
1 Meter: HK double > medium Explosive Arc > HK double > Shadow Explosive Arc > Shotgun Blitz ender (46%).
In Booster body and Blade body, repeat 0-meter combo and use Shadow Crescendo ender (Booster: 50%) or Shadow Allegro ender (Blade: 54%)
2 Meter: HK double > light Shotgun Knee > HK double > Shadow Explosive Arc > Shadow Explosive Arc > Shotgun Blitz ender (52%).
In Booster body and Blade body, repeat all-purpose 1-meter combo and use Shadow Crescendo ender (Booster: 56%) or Shadow Allegro ender (Blade: 60%)
( Damage calculation notesThese damage numbers were achieved after medium Shotgun Blitz opener, followed by a counter breaker. Keeping the initial combo as small as possible helps isolate the counter breaker damage, but this is an unlikely scenario in real matches. You can expect your damage to be much higher if you counter break in the middle of a normal combo.)
Notes: ARIA's kick doubles are faster than her punch doubles, so they must be used for these combos. Explosive Arc linkers do much more damage than Shotgun Knee linkers, but they take up an odd amount of time, so Aria is the only character in the game that likes to use medium linkers over light linkers in her counter break combos. The two-meter combo needs to squeeze in some shadow moves, though, so we make use of the faster Shotgun Knee linker here.
ARIA is unique in that her optimal punish depends on the body she is wearing. The main combos listed work in all bodies, so if you default to those you will do okay damage (and in Bass body, you have no choice). Blade body has access to the damage ender, so always use that when it is available if damage optimization is your goal. In particular, Shadow Allegro and Shadow Crescendo are preferred uses of meter over the Shadow Explosive Arc linkers.
ARIA is actually three characters in one. Unlike other characters who have two health bars, ARIA has the same total health pool split across three separate bodies, each being two-thirds the length of a normal health bar. The opponent must defeat each body to win a match against ARIA. ARIA's upper body changes appearance to signify which body she is wearing, and each form comes with a unique special move and movement option. Aside from a few specific normals in Blade body, ARIA's normals are the same across bodies, and she always has access to her Shotgun Blitz and Explosive Arc special moves, which are her only linkers. This means each body provides a unique flavor to ARIA but certain strategies and most combos are universally applicable.
If ARIA loses her health bar while wearing a body, that form will be permanently destroyed for the rest of the match, and ARIA will start the next round with a new body and be forced to fight on with her remaining forms. If all three forms are killed, the match is over. Interestingly, ARIA does not gradually recover potential damage on her active body like every other character; only the bodies she is not wearing are able to regenerate white life. If you are fighting a player who likes to perform resets or inflict lots of white damage, or if you find your current body's health low, you will have to switch bodies by pressing PPP or KKK. ARIA can switch in a neutral state or during a combo, which acts as a combo ender. If you switch in neutral, the switch animation begins with a brief period of invulnerability, but quickly becomes very punishable, so you will have to find ways to switch when your opponent is not near. As a bonus, whenever ARIA switches bodies, she removes all status effect cursesExamples include Kan-Ra's slow curse, Spinal's shadow meter and instinct curses, and Cinder's burnouts. she has incurred.
The bodies that ARIA is not wearing will float behind her as drones, and she can summon a drone to perform an attack for her with the 
+HP or +HK command normals. Termed calling an assist, each drone will perform a different predetermined attack which can protect ARIA's approach and make her safe, or force the opponent to block while ARIA performs a tricky mixup. Because assist calling is technically a command normal, this means you cannot call assists in the air, or while other normals or specials are being performed, but the assist call is very fast and ARIA is allowed to have multiple active assists at the same time. However, each drone can be hit by a single attack at certain points during its startup, active frames and recovery, and if a drone is attacked, the body form representing the drone will take massive damage (2.5x the strength of the attack). If a drone assist takes enough damage, it will die, and ARIA will lose access to that form, just as if she had died while directly wearing that body. Calling assists in ways to prevent punishment is important to learn as an ARIA player.
More importantly, ARIA can hover in this form by simply tapping and holding the up direction at any point after the apex of her jump, and she can steer herself horizontally in the air while her hover is active. If she crosses over an opponent, she will turn around, which effectively makes her regular jumping attacks act like cross-ups while she is in hover mode; if you tap up and let go immediately, she will turn around and drop to the ground facing her new direction. The Booster assist acts as a fast tackle which will push the opponent away if blocked, and cause a knockdown on hit. It is useful to gain space and time if your opponent is rushing in, or to put your opponent in block stun during a corner mixup. Booster assist is vulnerable after it is blocked before returning to ARIA's side, although if ARIA is pressuring the opponent, he will be unable to retaliate.
+HP). Interlude is a 20-frame overhead that is hard to react to, has long range, is special cancelable into combo openers, and has a fairly difficult to see startup animation. The Blade assist is an uppercut anti-air attack that is fully strike (though not projectile) invincible on startup and during active frames, making it excellent to cover the air in case your opponent jumps, or to blow through an opponent's attack if they try to escape ARIA's pressure. On hit, the Blade assist launches the opponent into the air, so ARIA is limited in her follow-up options.
The Bass assist is ARIA's best assist. The Bass drone fires a triple projectile at waist height, leaving the opponent standing on hit so ARIA can follow up with a combo, and protecting ARIA from most retaliations if she is interrupted on a mixup. This acts very similarly to a traditional "beam assist" in other fighting games, and Bass form has been placed as the last body so ARIA will have access to the assist while wearing both the Booster and Blade bodies. From far range, Bass assist is good at putting your opponent in block stun while ARIA closes in with a medium Allegro or a medium Shotgun Blitz. From close range, it is great to call just before your opponent rises from a knockdown, such as a throw or the Explosive Arc ender. In Booster body, you can hover on top of their body for a difficult left-right mixup, and in Blade body, you can mix up between low crouching MP and high Interlude. In all situations, any hit will lead to a full combo.
Medium Allegro in Blade body is not truly an opener, meaning you cannot perform auto-doubles or linkers after it, but you have enough frame advantage to easily land any manual of your choice, which will enter the combo system. This makes medium Allegro an important move in ARIA's arsenal, but typically only used in hit confirms or whiff punishes, since the move is very easy to shadow counter on block. The heavy version of Allegro launches for a juggle, but ARIA is often better off confirming a grounded combo instead.
While ARIA is a complicated character in the neutral game, her combo game is quite simple. Her only two linkers are the two universal special moves; there are no form-specific linkers to remember, so if you enter a combo, you can execute according to muscle memory without worry. Performing a manual after Shotgun Blitz has similar timing to Jago's Wind Kick (a little slow), while manualing after Explosive Arc is a lot like Laser Sword (a little fast). Explosive Arc is the damage linker and it is fairly difficult to differentiate the linker strengths. The Shotgun Blitz linkers cause ARIA to drop to her knees and bend over backwards in a recognizable pose while firing weapons and saying "Blitz". Her MK auto-double also fires weapons out of her knees, but you can distinguish it because she starts the animation standing up.
In particular, the first hit has a large (but late) window, emphasizing that breaking late is the way to go. The third hit, in my experience, is the hit you are most tempted to break too early, probably because of that large gap between the second and third hits. Don't deviate from the plan here, though; wait until after ARIA has stopped her forward movement and completed the firing of her shotgun before you press those buttons. And don't be fooled by the fact that hits 4 and 5 are a bit faster than the rest of the linker and jump the gun on breaking near the end.
It is also fairly important for you to not ignore the Upload enders, which cause a body switch. Because switching forms in neutral is very risky and often not possible, if you are low on health, I recommend doing a short combo and finish with an Upload ender to safely switch out. If you focus too much on the other enders, you will lose ARIA's bodies earlier than necessary, causing you to struggle later in the match. As a positive, the Upload enders actually do a surprising amount of damage, so you will not have to sacrifice much to switch. Allegro in Blade body is her true damage ender, and is probably the most common non-universal ender, but you will only have access to it one-third of the time.
+HP, a long-range low button with crouching MP, and a good crossup with jumping MP. When not in Blade form, these normals (except the overhead) still exist, but their range is considerably lessened and their utility affected. Crouching HP works as anti-air in all forms, and is her fastest heavy attack, so performing heavy manuals with this button allows extra forgiving timing. ARIA's kick normals are the same across all forms. Crouching LK is a long range, fast, chainable low attack that is good for pestering opponent. All normals involving MK will fire a shotgun out of her knee that acts as a projectile, meaning it can destroy most incoming projectiles. In particular, standing MK and crouching MK are important buttons for ARIA since they can act as very long range footsies pokes, and both buttons are cancelable into Shotgun Blitz for pressure on block or a combo starter on hit. All normals involving HK will fire a bomb out of her foot. Jumping HK, for instance, can act as a good long-range air-to-air as she kicks a grenade towards the opponent's air space.
Shotgun Blitz and Explosive Arc are ARIA's two universal special moves, which will see a fair amount of use in combos and in the neutral game. Shotgun Blitz hops over lows and combos after ARIA's best pokes (such as standing MK) and shadow Shotgun Blitz is her only projectile invincible move, while Explosive Arc can beat attacks with high hitboxes and the heavy version can leave ARIA at good frame advantage on block or hit. Both can be shadow countered; Shotgun Blitz is fairly easy, while Explosive Arc requires fast reactions and good timing, so mixing it up during your pressure will keep defenders honest. Of particular note, Shotgun Blitz's landing recovery is quite low, which means pressing a button at range and canceling it into the light version will not connect with the defender and leave you at a surprise range for a fast throw. If your opponent is waiting for Shotgun Blitz pressure to shadow counter, this technique can throw them off.
Booster form's hover mode can be great to fluster characters that prefer to fight you on the ground, and she can bait high recovery anti-airs by flying in and out of space and then punishing with a combo (or medium Crescendo from the air if you're at range). Blade form is exceptional at fighting on the ground, controlling space wonderfully with buttons and denying air access with light Allegro, the uppercut with perhaps the beefiest hitbox in the game. Bass form's zoning and hit-and-run tactics can frustrate slower characters or more impatient players, which can allow you to close the gap with her fast dash speed for some universally applicable close-range pressure. The understanding of the strengths of each form comes together a lot quicker than it might seem when reading a bunch of text, and I recommend performing combos with the Upload ender often at first; not only will you gain familiarity with the different forms, but you'll take less damage over the long run as your backup forms regenerate white life and soak damage in instinct for you. Learning to keep all your forms alive for as long as possible will serve you well at all levels of play.
After becoming comfortable with each form, the next step is learning the application of each assist. Unless you switch early, you'll start every match in Booster form with your other two assists. As mentioned, Bass assist is the one you should focus on first, since you will have access to it during both Booster and Blade form, and it's the assist that can create the trickiest mixups that additionally lead to full combos. Experiment in the corner by knocking your opponent down with a throw, calling Bass assist quickly, and then preparing for an overhead or low mixup (in Blade form). When you're at far range, calling Bass assist will let you perform a heavy Shotgun Knee to close the gap and prevent your opponent from moving away or attacking. If you are pressing footsies buttons at the mid-range and you don't want your opponent to jump over them and start a combo, call the Blade assist to protect the air while you try to engage him. There's no doubt ARIA is a deep, rewarding character, but unlike some other advanced characters, you can begin applying the strategy in layers and have success without needing to jump feet first into the deep end. You'll always have to be cautious of ARIA's smaller health bar in each form, as one counter breaker or knockdown could cost you a body, but the fun factor in switching forms and moving around the screen in multiple different ways throughout a match makes ARIA a shotgun blast to play.