Originally, Ash would receive the damage that the Pokemon experienced due to Aura Fusion, and now the Partner form also adds damage to Ash, meaning the pain Pikachu felt, Ash bears it doubly.
However, the rewards gained by bearing such a cost are remarkable.
On one hand, Pikachu's own strength is enhanced, the double buff amplifies Pikachu's power, directly boosting Pikachu from Gym Peak strength to be comparable to a Champion.
This leap is terrifying; even the Aura Power stacked up can only barely bring Pikachu to Elite Peak when reaching physical limits.
But now, the Partner form forces an upgrade on Pikachu's original basis, propelling his strength to the Champion level.
Initially, given Pikachu's current physique, he had no way to improve, but the principles of the Partner form and Aura Power addition differ.
While the Partner form enhances strength, it's not just a simple energy boost; it's an all-round enhancement.
All forces, including the physical body, are comprehensively enhanced, and this enhancement is quite mystical. Previously, when strength was weak, the enhancement was a minor stage, now reaching this level still offers a small stage improvement.
This disregard for rules in enhancement is somewhat more advantageous than Aura Power, not to mention Ash's Aura Power seems terrifyingly strong due to Ash himself being strong!
If Ash weren't that strong, the Aura Power boost would have been severely limited.
Moreover, the enhancement of Aura Power greatly depends on the Pokemon's ability to withstand; for example, when Monferno evolved initially, he couldn't withstand the peak Aura Power enhancement.
Eventually, he could only be enhanced to Elite Advanced Level, and even at that level, he couldn't utilize his strength properly...
Overall, although the enhancement of the Partner form and Aura Power seems more intense with the latter, genuinely speaking, the former is more advantageous, as it provides a side-effect-free minor level boost that can be stacked on any improvement.
So, what is the cost? The cost is on Ash himself, it's tremendous, no need for further explanation.
Apart from this benefit, another advantage is that Ash bears more damage, so relatively, Pikachu receives less damage.
The damage caused by the opponent's Pokemon is constant; Ash bears more, so Pikachu naturally bears less, meaning this time the Extreme Speed roughly caused only one-third the usual damage.
Of course, at Pikachu's current level, if he directly received Champion Advanced Level damage, even one-third might make him dizzy, possibly unconscious till night.
And now, Pikachu slowly stood up after falling from the barrier, Cynthia witnessed this and a hint of surprise emerged on her exquisite face.
"He didn't fall? It's somewhat different from what I imagined... Could it be that, apart from attack speed, that force can also enhance defensive strength?" Smart as Cynthia is, she's been studying the enhancement of Ash's Aura Power.
Though the strength amplification seems absurd, it's not without weaknesses, the primary being physical strength, secondly defense, then the negative impacts on the Trainer.
Leaving physical strength aside for now, given they've just started battling, exhausting physical strength through attrition won't occur in a short period, but defense... If Pikachu's defense hadn't changed, the recent Extreme Speed theoretically should've badly injured or KO'd him.
Even if not KO'd, he wouldn't appear unaffected like now unless Pikachu's defense leveled up to his current energy stage.
The harm on the Trainer level is evident, seeing Ash's condition, the Extreme Speed inflicted substantial damage too, but Cynthia isn't worried at all; this is the guy whom her friend calls a warrior capable of battling deities.
Even enduring small harm won't have any impact.
"Such fast speed, it feels a bit challenging, right Pikachu?" Ash said, clutching his stomach, half-squinting towards Pikachu.
"Pika Pi." Pikachu stood up supporting himself from the ground, nodded solemnly.
This time the opponent is the greatest gap he's faced, not just in terms of strength, even the speed he's most proud of falls short against them.
The recent Extreme Speed, visible in detail under Ash's Aura Power detection, still made Togekiss's movements seem slow-motion, whereas it looked paused to him.
Even predicting Togekiss's landing point, he couldn't dodge because his movements were too slow compared to Togekiss.
Helplessly, Ash and he could only stir the energy within and use Thunder for defense.
If hit directly by them, it wouldn't just be minor injuries, the gap between their levels is immense.
"First, find a way to reduce their speed, Pikachu, use Zippy Zap and then Nuzzle!" Ash quickly figured out the method to tackle the opponent's speed in less than a second of pondering.