Essence ofSword Art Online

You gain a free age and appearance change to whatever you want. You may also be any humanoid races in Alfheim Online.

You become really good at videogames, especially VR and AR ones. You are also incredibly good at applying RL skills into the videogames, such as swordsmanship letting you learn Sword Arts better and faster.

You gain superhuman reflexes.

You are genius in anything related to electronics, software, and code, such as being able to create full game worlds and even actual sentient AI. You could eventually even make robot bodies for those AI.

You have access to Sword Skills made real and can even create your own. This also comes with high levels of skill in actual swordsmanship.

You have access to real versions of Alfheim Online’s Magic and Underworld’s Sacred Arts.

You may have any Sword Art Online characters of your choice become your companions and may choose what relationships/history you have or will develop with each of them (being lovers, friends, etc.), if any, meeting them in positive circumstances. If you companion Yuna, you may merge her real and AI selves into one. Companioned AI characters are materialized as real versions of their digital selves. Likewise, companioned human characters are merged with their digital avatars (SAO, ALO, GGO, Underworld, etc.) made real, if any.

Optionally, you may Self-Insert into Sword Art Online or a variant (like a fanfic). You may choose when, where, and what world. The specifics are up you; maybe you get dropped in (default), maybe you insert yourself into or replace a certain character, maybe you get reincarnated, maybe you get merged with a local counterpart of yourself, etc.

If you Self-Insert into the above via an Essence or other means, you are guaranteed to meet the chosen companions in-universe (resurrecting them if they are dead by the point you enter the story, which may draw attention).