To counter a blackhole, i propose Luffy inventing a haki-based or VoAT-based method to break the limit of physics applying to his body without needing his Devil Fruit..thus achieving The State of Tachyon, with speed truly faster than light.
Wiki:
A
tachyon (
/ˈtækiɒn/) or
tachyonic particle is a
hypothetical particle that always travels
faster than light. Physicists believe that faster-than-light particles cannot exist because they are not consistent with the known
laws of physics.
[1][a] If such particles did exist they could be used to send signals faster than light. According to the
theory of relativity this would violate
causality, leading to logical paradoxes such as the
grandfather paradox.
[1] Tachyons would exhibit the unusual property of increasing in speed as their energy decreases, and would require infinite energy to slow down to the speed of light.
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In this headcanon i can imagine Luffy's fist becomes both intangible and having infinite energy output, penetrating or even phasing through Teach's Yami Vortex lol