As for completing the world task by deleting skills, the cost-effectiveness is too low.
After that, he didn't really take the ocean system enhancement route but instead followed the regular land battle enhancement route.
However, he was prudent, considering both land and sea, so when choosing skill sets, he picked those that could be used on both land and underwater.
Many skills are incompatible with water.
For example, flame skills, when entering the water, most flame skills can't function.
Similarly, a land acceleration skill like [Gale Step], is basically useless in water.
After all, [Gale Step] requires running to be effective, and you can't run in water.
Of course, it's not completely impossible to run in water; if combined with another skill [Underwater Walking], you can run on the seafloor when used with [Gale Step].
However, this combination has significant drawbacks in the ocean system enhancement route.