Elle Watson/Relationships

Kinji Tohyama
Elle (when crossdressed as L. Watson) was at initially prejudiced against Kinji because she was jealous of him for earning the respect and feelings of Aria, her arranged fiancee. As such, they were at an emotional impasse against each other where they appeared not to get along during the time period Elle was keeping her secret from Kinji. This included telling Kinji to stay away from Aria, driving a wedge between them, and isolating him at Butei High making his life a living hell. Eventually, the two would would fight each other after Watson kidnapped Aria causing Kinji to go into Hysteria Berserk Mode, where Watson was shown to be able to stand her ground against Kinji and almost killed him. However, Kinji was able to defeat her by using a new technique, which she almost fell to her death before being saved by him.

After Kinji saved Elle's life and found out she was a girl raised by her father to be a boy in preparation for their arrange marriage to Aria, he treated Elle more femininely while under the influence of Hysteria Mode causing her to develop an interesting amount of feelings for Kinji. Also, Kinji forgave Elle by allowing her to be a contracted medic for Team Baskerville and would use her actual first name when alone. In addition, she was surprised when he would not seek any vengeance against her.

Elle then began to act flustered when around Kinji, but would deny it, implying she may actually like him. As such, Elle requested Kinji to do shock therapy session so she could feel more feminine, undo her male upbringings, and get Kinji to be more like a man due to him not taking advantage of a girl who wants to be with him. Also, Elle would confess to Kinji that as she was growing up she would imagine herself being a girl when watching movies and would want to dress up as one in front of the mirror. In addition, during their shock therapy sessions, Elle would go as far as to strip down into her undergarments in front of Kinji, perform intimate acts with him (i.e. role playing), and even kissed him on his cheek repeatedly while muttering "I like you." The fact Elle chooses Kinji for her shock therapy shows how much respect and emotion she potentially harbors for him.

Aria H. Kanzaki
Elle was formerly Aria's fiance, although it was arranged marriage decided by Aria's grandmother. However, they had never met prior to the incidents of Volume 8 with Aria even confessed that she was doubtful of Watson's mere existence.

While Watson used a suave and smooth tone in attempts to win over Aria similarly to how Kinji would act in Hysteria Mode, it is unknown if Elle's masculine upbringing extended actually had some sort of feelings for Aria above the boundaries of friendship.

Riko Mine
Perhaps its due to both of them not knowing who each other's respective ancestors are, but neither of them seem to particularly like nor dislike each other. They can be considered to just have a mutual friendship.