Do the other characters already know how they present themselves? Do they prefer to have pronouns/names change depending on how their gender currently is?
If the other characters don't already know that the character is genderfluid or what their pronouns are then there should be a bit of a discussion depending on the world building. Shapeshifter=fantasy comic I assume? In this world, is gender fluidity pretty standard or is it rare? Will the other characters understand without more information given to them?
Is there any discrimination in your world? Would this character openly share that they are gender fluid to new people or is it something they keep private until they know the other characters more? Is it widely understood and accepted so they feel no need to keep a part of themselves private?
Just some more info is needed about your characters and comic to give any kind of specific advice 
