|a sentimental fondness (esp in the phrase have a soft spot for)|
soft spot n.
A weak or vulnerable point, as in That's the soft spot in his argument. [Mid-1900s]
have a soft spot for. Have a tender or sentimental feeling for, as in Grandpa had a soft spot for Brian, his first grandson. This expression, first recorded in 1753 as "a soft place in one's heart," uses soft in the sense of "tender."