Get familiar with HoloEasy.
HoloEasy is an open-source library for creating holograms in Minecraft that uses ProtocolLib (or PacketEvents) to handle packets. This allows for greater performance as the server does not have to manage these entities.
HoloEasy only uses packets instead of registering the entity in the actual Minecraft server.
No, the API wasn't created for only Kotlin users, but rather to provide a clean, fluent API that works well in both Java and Kotlin environments.
For library and plugin devs.