The story has elements of fantasy, adventure, exploration, and mystery. She gradually makes him smaller and smaller as the game goes on using her smartphone. The player takes on the role of Makoto, a boy visiting his old childhood friend Chieri. A Ko-fi page has been set up to accommodate this. The artists and developers of Sizebox are not paid regularly for their work and so depend on donations.

It is also common for players to create art and videos related to Sizebox.

The community at large contributes enormously to the game's library of assets, converting and creating models, props, stages, and scripts daily, the vast majority of which are free. Since then, Sizebox has seen numerous voluntary developers come and go, contributing to each update and keeping players informed on Discord and Reddit. In December 2017, an update was posted on the Giantess City forum, informing the community the game's development would continue without Aiiko at the helm. Over time, new developers would join Aiiko in improving the game and a Discord server was set up to coordinate these efforts as well as provide a hub for the community. In the following months, Aiiko would develop the game further, introducing new features, many of which were suggested by the community. A free alpha version was released and immediately gained notoriety for the sheer degree of freedom it offered the player. The game was announced in 2017 by Aiiko who had been working on it as a passion project. More features are to come in future updates. Other features include destructible city generation, usable vehicles (cars, planes etc.), scene/model saving, and scripting for custom animations.

The difference in scale between objects in the game can be incredibly huge, a popular feature that is possible partly because of the game's overall simple, even cartoonish aesthetic. Prop and character size can be adjusted via menu or with an in-game shrink ray, and can be set to change over time (gradually shrink, grow in spurts etc.). The player can move freely about the environment, controlling the speed of characters, animations, poses, and most notably their scale. Some of these items were originally made for the game, but most have been converted from existing assets. Players can build interactive and dynamic scenes in a range of settings (a blank plane, an island, a house etc.) using imported props, models, and sets provided by the community.

Furry model sizebox