Ichigo has BANKAI. That could take out Starscream pretty fast. Just a regular Getsuga Tenshou would beat him. Ichigo wouldn’t lose much time on his account. Starscream and Ichigo aren’t in the same league. Ichigo wins.
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Unfortunately for Ichigo, Starscream possesses the uncanny ability to not be killed. No matter how he dies, Starscream will come back in any form, and kill him in any way imaginable.
It is tough for Starscream to die since Megatron’s always saying he will but never gets him, but Ichigo can just destroy earth and that would be it for Starscream. Unless Starscream escaped the explosion, but Ichigo would still get him.
Ah, but Starscream can just posses this Ichigo fellow, make him run off a cliff, and leave his body before he hit the ground.
Ichigo is a soul reaper. Which means Death God. In Shinigami Form Ichigo is dead and can’t be possesed by ghosts. He destroys ghosts on contact.