A technical character is a character who is not all that easy to use because the level of technique required to use them is rather exacting.
Oftentimes, technical characters (in the hands of players who have mastered them) can be high-tier characters with good capabilities for success. They may break the game’s balance, but first, they still require good technique.
True technical characters are not for beginners by any stretch. Sometimes, an newbie may not even be able to move them. They exist strictly for the enjoyment of advanced players.