Here's how I imagine Akira in Smash after getting about halfway through Astral Chain. Using all the Legions might be a bit much, but take it as an ideal fantasy or whatever:



Neutral Special: Holding the button opens up the Legion Wheel, similar to Shulk's Monado Art Wheel. Unlike with the Arts, I imagine each Legion would have the same cooldown. Pressing the special button after summoning a Legion sends it forwards a fixed distance to perform an automatic combo. This combo can be canceled by pressing the button again, which summons the Legion to your side. Summoning the Legion to your side while the opponent is touching the chain could have an effect of some kind? Unlike Arsene, another stand-like helper character, the Legions have hurtboxes and can be hit, which makes the cooldown timer tick down faster. Using normal attacks while a Legion is out makes them perform their own normals.



Up Special: This move is the same regardless of the Legion. You fling them diagonally upwards using the chain and they pull you along with them. Think Ice Climbers' Belay.



Down Special: X-Baton form change. For simplicity's sake it might be better to change only between the gun and baton forms, limiting the gladius form to smash attacks where the X-Baton changes to it automatically. The baton form is pretty simple, offering a decent disjointed range to the attacks that use it (some normals and aerials might be kicks?) and having decent frame data. The gun form has longer range, but deals less knockback, not being able to kill until really high percentages. For balance reasons might not deal knockback at all when hitting at max range.



Side Special: A Legion specific attack. This is based on my knowledge of each Legion so far, so there might be more fitting moves, but these are my suggestions for now. Using each move uses a chunk of the cooldown meter.

The Sword Legion uses a sword slash with big range. Holding down the special let's you use the control stick to determine the angle of the slash, altering the hitbox and knockback angle.

The Arrow Legion shoots arrows straight upwards through the top of the screen, and after some time the arrows land a fixed distance away from where they were shot (not all in the same exact spot, more like forming a mat of arrows after they've landed).

The Arm Legion unleashes a barrage of 3-5 punches. If they hit, it executes the rest of the move, continuing the barrage and finally launching the opponent upwards with significant KO power. Think Mii Brawler's Flashing Mach Punch. This move may actually work like the "L-move" of the Arm Legion in Astral Chain, where it becomes an armor around you. This would also give the move an additional property of stalling you in the air, just like how it makes you float in Astral Chain.

The Beast Legion dashes forward and if it hits an enemy, binds them with the Astral Chain, preventing them from moving for a time. Works as a command grab. If the Beast Legion is hit while dashing forwards, the move is canceled.

The Axe Legion forms a protective barrier around itself (and Akira if executed while close) that reflects projectiles and absorbs attacks. Can be held for a time, and when released, unleashes an explosion if it was hit with an attack. The power of the explosion depends on the power of the attack that hit the barrier. Note: I haven't unlocked the Axe Legion yet, so this is probably the most inaccurate representation since it's only based on what I've observed from Max's use of it and what it will be able to do according to IRIS.



Final Smash: activates similarly to Robin's, only instead of summoning Chrom they summon their twin. If the twin's attack hits, activates a cutscene where each Legion attacks one after another and Akira delivers the final blow together with his/her twin.