#[05AB1E](https://github.com/Adriandmen/05AB1E), <s>7</s> <s>6</s> 4 bytes

Code:

    lIl-

Explanation:

    l     # Convert the first character to lower case
     I    # Get the second line of input
      l   # Convert the second line of input to lower case
       -  # Loop over the second line of text and substract each char from the first input
            For example: "abcde""ba"- would result in "cde"

[Try it online!](http://05ab1e.tryitonline.net/#code=bElsLQ&input=RQpUaGlzIGlzIGEgbGlwb2dyYW0u)

Truthy is when the current letter is outputted. Falsy is when nothing is outputted.