Shapeshifting or Mimesis (擬態, Gitai) is an ability which grants the user the ability to change themself into another being.
The only person to display this power in Tiger & Bunny is Ivan Karelin, AKA Origami Cyclone. He has the ability to shapeshift into whatever he touches. He can copy the voice but not any attributes such as strength or NEXT powers of a person he changes into. He is also able to use his own voice when transformed into someone else.
Ivan has also demonstrated the ability to camouflage himself against a brick wall and wanted poster. This implies that his power isn't limited to living things, and that he is able to shapeshift into various objects and items.