The most common and most likely answer to this crossword clue is the 5 letter word SOFTY
S
O
F
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More clues leading to the result SOFTY
Buddy explains!

The straight part
We know that "sentimental person" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sentimental person = softy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SOFTY mean?
SOFTY noun- A weak or sentimental person.
- Somebody who finds it difficult to scold or punish.
- A software expert who is ignorant of the workings of hardware.
- A soft drink containing no alcohol.