I say "hardest" because in all honesty, I find the EIR fight in ??? Area much more annoying.
In any case, here's me doing the insane, as there was a question I couldn't help but want an answer to: Is there an opportunity for the Metal Attacker to fully charge the Accel Blast during the fight against RISING GARUDA? Well, as it turns out, there is! The idea is to whittle down RISING GARUDA's life down to a point where one volley of Homing Missiles will be enough to force it into its last-ditch attack pattern, and the safest pattern that I've found (if there are any others where I think it would be safe, anyway) is to do it during the lightning attack (telegraphed with an ECG pattern in the background) after clearing some space for yourself to begin charging.
Of course, this is completely impractical; the easiest way to finish that fight is simply to use Thunder Break on the final pattern once the second part of the attack commences, as RISING GARUDA will fly straight into your line of fire trying to ram the MA. But like my video on the game's harder final boss, I did the preceding fight in a way where you can learn how to dodge the boss' attack patterns and also deal massive damage against them, so I hope those of you watching this video get a bit of practical advice from this boss showcase, too.
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