Seishirou Tsugumi is one of the main characters from the Nisekoi anime and manga.
Chitoge's childhood friend, Claude's protégée and a deadly hitman. She has a very obvious crush on Raku but lies by saying that she absolutely hates Raku and doesn't want him to be anywhere near her.
In the XP4 fics, Seishirou is part of the Heroes Coalition as a trainee. She also attends the Vanguard Academy as a student.
Tsugumi has fair skin accompanied with very short, navy-blue hair and radiant, red eyes. She is said to look very masculine. In fact, Tsugumi was mistaken to be a boy by many people when she first enrolled into high school, due to her looks and her uniform. Despite this, her breast size is an E, and is actually still growing. She is usually seen wearing a school uniform consisting of the following: khaki pants and a white shirt with a red necktie with a thin orange lining that goes up to her chest. She wears a blue blazer over it and wears brown shoes. Tsugumi also wears a blue-ribbon on her head that was given to her by Chitoge to make her look more feminine.
Once, she was shown wearing a girl's school uniform, which she was forced to wear by Chitoge. She says that she avoids feminine clothes, including skirts and dresses because they are hard to fight in and are embarrassing to wear. However, when Chitoge asks her to wear them occasionally, she can't help but accept. During a visit to the beach, she wears a skimpy red strapless bikini, much to her embarrassment.
Another case has also been revealed, in which she follows Raku Ichijō, on his date with Marika Tachibana, wearing a purple dress, laced with white, with a brown belt around her waist. She is seen wearing violet colour shoes with lace socks underneath and a matching headband with a small bow on it. She also wore a wig with pigtail braids.
Tsugumi is exhibited as masculine and aggressive. As a sworn member of the Beehive Gangsters, Tsugumi is very loyal towards the organization, especially its mistress, Chitoge Kirisaki, as with all its members. Tsugumi is mostly portrayed as serious, focused and somewhat mild-mannered. However, after befriending Raku and co., Tsugumi reveals a more feminine and emotional side. Furthermore, Tsugumi is a shy individual and becomes greatly flustered and embarassed as shown when her mistress would resort her to wear more feminine clothing or when confronted by praise or compliments (especially Raku's). Tsugumi is also rather frank and direct, never hesitating to speak out her mind. Tsugumi can also be playful and cheerful at times, proving that she can be sociable.
Tsugumi is dumbfounded by the concept of love, which is shown when she is oblivious of what a love letter is and has no knowledge towards the celebration of Valentine's Day. On the contrary, Tsugumi is quite knowledgeable in how to confront her emotions and how to act accordingly with it which was evidenced when Raku would usually come to Tsugumi for "love advice".
Despite Tsugumi's masculinity, she is usually the target of being groped by her female friends due to her buxom physique, leading Tsugumi to develop breast complex.
- Immense strength: Tsugumi is able to crack walls by banging her head on it and able to destroy a portion of a wall with a single kick.
- Skill with guns: Tsugumi is shown to be capable of reassembling a disassembled gun and firing it with remarkable speed - even when blindfolded.
- Skill in cooking: Tsugumi is shown to be very good in cooking, and was also remarked by Raku.
- Like Paula McCoy, she is scared of ghost stories/scary things.
- Initially, during her introduction, Tsugumi was showed extremely manly, with no visible breasts. However, once her gender was out to the audience, she was given the largest breasts much bigger than any other girl in the series as a sign of her feminine interior.
- It was said that Claude was the one who gave Tsugumi her the name 'Seishirou' and Chitoge Kirisaki who gave Tsugumi her surname.
- In Chapter 68, Raku Ichijō told her that she was the first girl who gave him chocolates (though it was just obligatory chocolates).
- As the story progresses, Tsugumi began to show her feminine side more than her masculine side.
- Claude doesn't know that Tsugumi is a girl until the last chapters.
- Tsugumi has a gun hidden in her right sleeve.
- The gun that Tsugumi has hidden in her sleeve is a Beretta M92 in the manga. In the anime, it's an S & W M66.
- In the duel Tsugumi had with Raku in Rival, Tsugumi used an RPG-7, M249, Remington M870, and several other large firearms.