Well, correct. Another way would be through touch. By maintaining contact with something, you release Keigoku into it to the point that it corrupts the core and momentarily turns it into Keigoku. Of course, this isn't currently possible and only the overview of the idea, but in theory, it could be possible. Anyway, moving on.
Going with the second method, I developed a way to firstly augment our taijutsu prowess by using Keigoku and to also bypass a restriction legally.
( Dark Convergence ) - Kuro Shuusoku
Rank: A
Type: Supplementary/Offensive
Range: Short
Chakra Cost: 50 (+10 per turn active)
Damage Points: N/A (+15 to opponent for every taijutsu blow landed)
Description: The user will focus and open 4 human sized portals, one on each side of his body and a metre away from him, allowing massive amounts of Keigoku to pass through the portals and flow onto him. This large influx of chakra reacts with the symbol that every clansman has branded on them and causes it to go haywire, so to speak. Instead of projecting and guiding Keigoku, it causes the Keigoku to travel inwards, filling the user's tenketsu with keigoku, warping it's usage and causing the chakra to flow inwards, preventing Ninjutsu or genjutsu usage as long as it is active as the chakra cannot be molded correctly. As the Keigoku flows inwards, it corrupts the user at the very core, literally turning him into a solid manifestation of Keigoku, causing building damage to the user over a series of turns. Taijutsu attacks are augmented through the usage of this, adding properties of being exposed to Keigoku with each strike that lands.
Unfortunately, there are more drawbacks than benefits; the longer the user has this jutsu active, the more at risk he is of fatally harming himself from the reverted flow of chakra. If active for longer than two turns, upon deactivation the user can only use taijutsu attacks for two turns as it takes time for the user's tenketsu to start it's correct flow. The user also can not use any Keigoku techniques of S-rank and higher while this is active. While this is active, the user is vulnerable to sealing jutsus that seal away elements and/or jutsus.
The Nekura requires special training and must be Black Knight or above to utilize this jutsu. To add to this, this jutsu can only be used twice, lasting at a maximum of 3 three turns each turn with a build up period of at least 2 turns in between usage.
Now analyze it and tell me everything about (weaknesses, strengths, best methods to use it with, combating it, using in combos, etc etc).