When the Puzzle was finally made, Yami took complete control of Yugi to challenge someone to a shadow game (This is never mentioned in the second series). Yami took control of Yugi on many occassions, but Yugi never told anyone about his blackouts, because he was afraid that his friends would desert him. Eventually, everyone came to understand the spirit of the Millennium Puzzle, and he and Yugi soon became friends. In both the Japenese manga and episodes, Yugi calls Yami 'Mou Hitori No Boku' (Another I) while yami calls Yugi 'Aibou' (Partner). In the English dub they merely call eachother by there names (Yugi and Yami).

Yugi is a very skilled duelest, but hardly ever fights a serious/lifethreatening duel without fusing with his yami. Fusing with Yami makes him much more confident and a much better duelist, though he is slowly starting to take after his darker half when dueling. Yugi is polite, shy, kind-hearted and possibly the most anti-violent person in existents, while Yami shows a little less mercy to enemies. When there is danger involving his friends, however, Yugi's attitude can sometimes do a complete 1-80 without Yami's help. When his friends are involved, Yugi is willing to put his life on the line and fight for them, as long as they are out of harms way.

As the series' have progressed, Yugi has become more confident and couragous, as well as becoming a much better duelest. Now and beforehand he has had a strong hate for bullies and villans, but at times seems to try and see the best in people. He is quick to forgive if he knows someone is sorry, and is very understanding.