sham, temporary, interim, assumed (name), informal
仮 centers on something that is not the real or permanent version: a temporary stand-in, an assumed name, or an informal arrangement. The idea of 'sham' follows naturally from something being a substitute rather than genuine.
仮 is the modern simplified form of 假. The older form combines 亻 (person) with a phonetic component that also carried the idea of borrowing or not being genuine. The modern 反 shape is a simplification and should not be treated as the original historical component.
A person 亻 beside 反 (which looks like a hand turning something over) suggests someone flipping roles temporarily: a stand-in or an assumed identity.
For カ, imagine a temporary cardboard cutout of a person: 'card' -> カ, and it's just a sham stand-in.
even if; no matter (what); if; though; although; supposing; supposing that; -ever
mask
temporary; provisional; interim; tentative
imagination; supposition; virtual; potential (enemy)
supposing; even if; granting that; for argument's sake
Kamen Rider (TV series, the titular character)
hypothesis; supposition; assumption; tentative theory
assumption; supposition; hypothesis
kana; Japanese syllabaries (i.e. hiragana and katakana)
alias; pseudonym; pen name; nom de plume
costume; fancy dress; masquerade; disguise
katakana; angular Japanese syllabary used primarily for loanwords
temporary construction; temporary establishment; provisional construction
nap; doze
hiragana; cursive Japanese syllabary used primarily for native Japanese words (esp. function words, inflections, etc.)
temporary name; provisional name
provisional disposition; temporary injunction
false (symptoms)
releasing on parole; conditional release
feigned illness