The reason for this is fairly simple.
Most characters in the game are static 2D illustrations, while Jun uses a 2.5D / Live2D-style model that allows her to move and interact with the player.
If you are familiar with VTuber Live2D models, it works in a similar way, but integrated directly into the game.
Because of this, Jun’s model has to be designed in a way that supports interaction and animation, which makes it more complex than standard 2D character portraits.
Adding too many complex movements or poses to a Live2D model would make it much harder to implement interactions and new scenes, which is also one of the reasons why new interactive or NSFW scenes can take longer to develop.
However, in situations where Jun does not need to be interactive, such as certain story scenes (for example, the recent beach scene), the developers may instead use regular 2D illustrations with facial expressions, similar to how the other characters are presented.
