|Full Name||Watanabe Mari|
|Family||Chiba Naotsugu (Boyfriend)|
|School|| First High School |
National Defense Academy
|Voiced By||Marina Inoue (Anime)|
|Novel||Volume 1, Chapter 2|
|Manga||Volume 1, Chapter 4|
|Anime||Episode 1, Enrollment Chapter I|
|Spin-off Manga||Volume 1, Chapter 2|
Naotsugu is Mari's boyfriend. She calls him "Nao". Mari loves and depends on him very much, as mentioned by Tatsuya that Mari's condition was getting better due to 'boyfriend effect' in the light novel.
Mari trusts Tatsuya and views him as a very capable individual, despite withholding secrets from her at times. Mari is one of the few individuals who teases Tatsuya, often flirtatiously, however he usually manages to ignore or turn around the situation, causing Mari (and sometimes a few others) to blush in embarrassment. Although technically his senior in the Public Morals Committee, she relies on him to organize the club room a bit more than she should.
During the Yokohama disturbance she discovered that he was a soldier who holds the position of Special Officer and learned of his regrowth ability, choosing to keep his secret. Though he is a second course student and an underclassman, Mari views Tatsuya as a friend and one of the few people she chooses to speak with on first name basis.
| In volume 17, Mari emailed Tatsuya for a private meeting after she met with Mayumi.
During meeting she asks Tatsuya what he thinks about Mayumi. Tatsuya answers without much thought that she is a talented magician and exceptional person. Mari does not like the response and asks again what he thinks about her as someone of the opposite sex; to which Tatsuya responds that she is a lovely person. Mari presses again that this is not what she meant; Tatsuya wonders out loud if she is referring to a kind of sexual attraction, which causes Mari to blush.
Mari explains that there are intentions to match Mayumi with Tatsuya; similar to the situation with Ichijou trying to force a commitment with Miyuki and Masaki. Mari says Mayumi has no clue what her true feelings are towards him and asks Tatsuya if he would consider dating Mayumi in secret. Tatsuya finally understands the situation and says he has no intention of breaking his commitment and promise to Miyuki. Tatsuya ends the conversation and pays the bill before leaving.
"That woman" is how Erika refers to Mari during the Nine Schools Competition Arc. Erika believes Mari is distracting her brother Naotsugu's duties and training; and generally being a bad influence on him. Miyuki immediately took the opportunity to tease Erika with being a bro-con, after witnessing the scene where that reference above was uttered.
Mari and Mayumi share a teasing, friendly relationship. In Volume 17, Mari tries to convince Mayumi that Mayumi actually likes Tatsuya.
Koutarou often teases her by calling her Nee-san, which peeves her so much that she resorts to some limited violence.
Their relationship was a strained one from Sayaka's side. Sayaka, as a Second Course student, resented the discrimination a lot of First Course students bear against them. Due to the ambiguous wording by Mari, while rejecting Sayaka as a sparring partner, a misunderstanding was born. It was turned into animosity, and exploited against Mari and the against discrimination of Course 2 students, by the Blanche leader (the former step-brother of Kendo club captain). Her misunderstanding was cleared after the terrorist attack on First High by Blanche members.
Mari treats Kanon as some sort of a younger sibling. Mari marked her out to be her successor as the Public Moral Committee Chief, which added to the already substantial amount of load in paperwork for Tatsuya.
Mari not only supports Kanon in succeeding her title, but never fails to harshly train her given the chance. This earned Kanon a knock on her head, during the bus trip to the AD 2095 Nine Schools Competition venue, when she failed to properly co-operate in fending off an impending disaster caused by a suicide attack. Mari brought the necessity of communication to Kanon's attention with Miyuki's example.