The key to caring for a sad person in a comic is to create a warm and understanding atmosphere. You could have characters bring the sad person to a peaceful place, like a beautiful garden, and have a heart-to-heart conversation. Or, show them doing something fun together, like playing a game or having a picnic, to take their mind off the sadness.
You could show them kindness and offer a shoulder to lean on. Maybe give them a big hug and tell them everything will be okay.