|“||This is my ship, and I'm its only captain||„|
|~ Tessa to Gauron|
Cpt. Teletha "Tessa" Testarossa is the tritagonist of the light novel and anime series Full Metal Panic!. She is the 16 year old captain of the paramilitary counter-terrorist force, Mithril. She has a huge crush on her subordinate Sousuke Sagara and is both Kaname Chidori's love rival and good friend.
Tessa is quite a short girl, standing shorter than both Melissa and Kaname. She has silver/platinum hair that she keeps in a ponytail and gray eyes. Her usual outfit consists of a light brown suit and skirt, the former of which she wears over a white-collar shirt and black tie.
Tessa is a very cheerful, bubbly and friendly young girl who deeply cherishes her subordinates on the Tuatha de Danaan and treats them like her own family. She especially cares for Sousuke, who she has a huge crush on. She seems to have no sense of personal space, often hugging Sousuke and once even trying to kiss him while he's asleep. She also frequently worries about him, particularly when he's out on a mission, and was by far the most doubtful about him being sent to watch over Kaname. She also has a habit of playing with her ponytail.
Tessa is very proud of her submarine, the Tuatha De Danaan, to the point that she celebrates the first-year anniversary of its building as though it were its birthday, even having a big party to celebrate. After she goes through a long struggle to reclaim the ship from Gauron, who hijacked it with the intention of having it destroyed, Tessa declares that the Tuatha de Danaan is her ship, and she is its only captain.
Being captain of the Tuatha De Danaan, Tessa is a very capable strategist. She displayed some very impressive military strategical skills at several points, such as the first two episodes of Full Metal Panic! The Second Raid, where she helps Sergeant Sagara escape death and also help their team get out of a tight situation in an underground operation. Also, during the last two episodes of the first season, she helps prevent the Tuatha De Danaan from sinking, and performs some very skilful actions to save them from destruction, not once, but twice from torpedo attacks. During the operation in Nanjing, Tessa figures out that the enemy is listening in on Mithril's communications and so can predict their every move, and manages to turn the tables on them by giving her subordinates contrary orders, showing that she is a capable leader.
Despite her innocent. air-headed nature, Tessa is also a very competitive person; it's noted by Kurz that whenever someone tells her that she can't do something, she takes that as a point to prove that she can. Part of this is due to an inferiority complex she has towards her older brother, Leonard, who would always one-up her when they were children e.g. he solved a complex problem when he was four that she did when she was six. Despite this, the two got along due to her looking up to Leonard, though as she got older she realised that this was far from a typical, healthy brother-sister relationship.
As kind as she normally is, Tessa also has a very clingy side when it comes to Sousuke; when Kaname mistakes her for Sousuke's girlfriend upon first meeting her, Tessa is so pleased that she ends up playing along, causing Kaname to believe that Sousuke is lying to her about Tessa being his captain. This side of hers reaches its peak in The Second Raid!, when she ends Sousuke's bodyguard mission, even denying him the opportunity to say goodbye to his friends, purely out of her jealousy towards Kaname, which results in Sousuke temporarily becoming a nihilist and self-admitted death seeker and Kaname nearly getting killed by Xia Yu Lan. Nevertheless, Tessa does have the sense to recognise when she goes too far and ultimately apologises for the latter incident, saying she acted like a spoiled brat.
Tessa was born on December 24, 1984 and is a child prodigy who achieved the rank of Captain by the age of 16. She was born in the USA's northeast to a family of Swiss and Austrian descent. It can be inferred that she is of Italian descent judging by her last name Testarossa. She travelled the world extensively as a child; however, she has spent a great part of her life living on submarines and Iams.
When she was younger, she lived in Okinawa for a while, while her father suggested she attend a Japanese school there, but as she did not mix very well with the other Japanese students, she was transferred to another school, this time on her father's military base.
Tessa is a Whispered (like Kaname), and thus is gifted in science and mathematics. When she was six years old, she had derived the answer to one of Albert Einstein's scientific theories. On a side note, her twin brother, Leonard Testarossa, did this at age four, giving her an inferiority complex, as she states in Episode 10.
She worked her way up very quickly in Mithril, and became Captain of the Tuatha de Danaan after being commissioned by MITHRIL. It is also speculated the knowledge found within her may have led to the construction of TDD-1, due to the fact that Gauron refers to the existence of a Whispered knowledgeable in the field of submarine construction. She also mentions having had a hand in the construction of its AI, Dana.