two, two radical (no. 7)
二 represents the number two. The radical sense is the same two-stroke shape used as a component in other characters.
two; 2
two
two persons; two people; pair; couple
never again
the Two Ise Shrines
carbon dioxide; CO2
killing two birds with one stone
halving; dividing (into two parts); bisection
secondary; of secondary importance
two-base hit; double
handsome man
second base
second-rate; inferior
two-wheeled vehicle
three-legged race
two out; two down (and one to go)
choosing between two things; two choices
double-dealing; duplicity; equivocation; double-tongued
the two houses of legislature
second baseman
instrumental duet; instrumental duo
in two equal parts
the first and second; a few
second (in a series)
二 is a simple ideograph of two parallel lines representing the number two.
Two horizontal strokes, one above the other, clearly show the number two.
For ニ, picture two knees (ニー) side by side: knees -> ニ, and there are two of them.