#include<bits/stdc++.h>
using namespace std;
// Numbers and string values
/*
Given two numbers n and k, find a string s of length n consisting of lowercase alphabets such that
sum of all the elements in the string is equal to k. If there are multiple possibilities find
lexographically smallest one. a=1,b=2,...
Input:
2
5 42
3 25
Output:
aaamz
aaw
*/
string solve(int n, int k);
int main(){
int t;
cin>>t;
while(t--){
int n,k;
cin>>n>>k;
cout<<solve(n,k)<<endl;
}
return 0;
}
string solve(int n, int k){
string ans;
for(int i=0;i<n;i++){
ans.push_back('a');
}
k-=n;
int i=n-1;
while(i>=0 && k>0){
if(k>25){
ans[i]+=25;
i--;
k-=25;
}else{
ans[i]+=k;
break;
}
}
return ans;
}