conditional – Comparison of two tables of unequal length

I have two tables, let's say

array1 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
array2 = {13, 4, 6, 20, 21};

I want to compare these two paintings by bike Table 1 through all the elements of Table 2. The output must be the position in each array where they correspond to a condition, where the condition Table 2[[m]]= table1[[n]]-1 is right. That is, the result should be:

output = {6.2}

Because in Table 2, $ 5-1 = $ 4. (Table 1[[6]]= 5 and Table 2[[2]]= 4). Until now, my code is

output = {Position[array1, #][[1, 1]],
Position[array2, #][[1, 1]]} & / @ (I have no idea)

Where the code on the left side of the card gives me the positions of a true condition. On the right side of the map, I do not know what to do.

To clarify a little, the code I want is similar to

output = {Position[array1, #][[1, 1]],
Position[array2, #][[1, 1]]} & / @ Intersection[array1, array2]

Except that I want the position of the element when table2 = table1-1 instead of when table1 = table2.