For the chocolate mousse, melt chocolate in a water bath or double boiler. Add the cream and stir with a wooden spoon. Let cool and pour into a whipping siphon. Place in the refrigerator and leave to chill for at least 2 hours.
For the fruit salad add grapefruit, kiwi, raspberries and blueberries to a bowl. Slice the ginger and add. Split the vanilla pod in half lengthwise and scrape out the seeds with a small sharp knife. Toss gently and refrigerate till serving.
For the mango swirls add water and sugar to a small saucepan and boil for 1 minute. Put mango and syrup in a blender and blend till smooth. Pour the mango mixture in a saucepan, add the agar agar and stir. Bring to the boil and cook for 4 minutes, stirring often.
Have a bowl with ice water stand by. Take the syringe and using the plastic tube, suck in the mango mixture. Plunge the syringe into the ice water and leave it there for 3 to 5 minutes.
Have 4 dessert plates ready. Push the air out of the syringe, then squirt a swirl of mango onto the plate. Repeat this several times to obtain a continuous circle.
Tip the rest of the mango puree in a silicone mold and fill only half to form semi balls. Refrigerate for 30 minutes.
To plate, add some fruit salad to the mango swirls. Test the whipping siphon by spraying a small amount into the kitchen sink. The foam should be like whipped cream. Spray some chocolate mousse onto each plate and add a mango semi ball. Serve chilled.