Well, keep in mind that the powered-people don't have thier powers active since birth. They all first started manifesting their powers shortly after a solar eclipse. There was one (in Hero's timeline) shortly after arriving. So Kensai's power would not necessarily have manifested before, this could (quite possibly) be the first time that it could even have taken effect since it is his first injury (that we see) since the eclipse in epi 1 of this season.
(it's late so i think i just talked in a circle, sorry if it rambles

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