Prefix Match with Flexible First Character

Background

Congcong is currently learning about string processing and has encountered an interesting problem that requires your help to solve.

Problem Description

Given a main string $S$ and a "word" string $W$, we'll say that $W$ matches $S$ if it appears at the front of $S$, except its first character does not need to match exactly. On a match, return the front of $S$ (with the same length as $W$), or otherwise return the empty string. The word $W$ will be at least length $1$.

For example, with the string $S = ext{"hippo\