Mamoru's personality was very brash at first, especially toward Usagi Tsukino and to her friends,such as Rei Hino.It was slowly revealed that his brashness stemmed from the fact that he was orphaned on his sixth birthday in a terrible car crash that left him with a bout of amnesia and therefore he had some trouble opening up to others on a deep level. He was often a target for the enemy, and suffered through amnesia many times between the first and the second season of the anime.
- In the anime, he had a brief relationship with Rei Hino though he did not seem to take it as seriously as Rei did; in fact, he seemed to merely accompany her on dates to keep her happy rather than through any great desire on his part.
- In the live-action series and the manga he had a more stronger relationship with Usagi even before they knew their memories of the past lives.Also he had a relationship with Hina but she broke up with him so he had a chance with Usagi.
- He and Usagi love each other so much that in the live-action seiries Queen Beyrl became soooo jealous that she decided that she shoud take him for herself.
- In both the anime and the manga he seemed to have dumped Usagi when he left to study in America, as he never wrote or called, and during this time Seiya pursed Usagi but this became because Galaxia took this starseed.