Accessing a character from int variable using pointer in C

Why the output of below code is -127. Why shouldn't it be -1?

#include<stdio.h>
int main(){
    int a = 129;
    char *ptr;
    ptr = (char *)&a;
    printf("%d ",*ptr);
    return 0;
}

It can be understood as follows:

We all know that the range of (signed) char is from [-128 to 127], now let's break this range into binary format, so, the bits required is 8 (1 Byte)

0 : 0000 0000
1 : 0000 0001
2 : 0000 0010
3 : 0000 0011
...
126 : 0111 1110
127 : 0111 1111 <-- max +ve number as after that we will overflow in sign bit
-128 : 1000 0000 <-- weird number as the number and its 2's Complement are same.
-127 : 1000 0001
-126 : 1000 0010
...
-3 : 1111 1101
-2 : 1111 1110
-1 : 1111 1111

So, now coming back to the question, we had int a = 129;, clearly 129 when stored inside the char data type it is going to overflow as the max positive permissible value is 127. But why we got -127 and not something else?

Simple, binary equivalent of 129 is 1000 0001 and for char data-type that comes somewhere around,

127 : 0111 1111
-128 : 1000 0000
-127 : 1000 0001<-- here!
-126 : 1000 0010
...
So, we get -127 when 129 is stored in it.