Step 1: Understand the phrase.
``Religion-related state'' here means the state’s constitutional identity is explicitly tied to a religion.
Step 2: Evaluate.
Pakistan is an Islamic Republic; Bhutan recognizes Vajrayana Buddhism as spiritual heritage; Sri Lanka accords Buddhism the foremost place.
Step 3: Identify the exception.
Nepal became a {secular} federal republic (2007 interim constitution; 2015 constitution).
Step 4: Conclude.
\[
\boxed{\text{Nepal (Option C).}}
\]