ISML 2008 #42(21-42)
A "Whispered" - one of a few individuals born with super-technology in their brains, so named because of the whisperings they hear as they mature. In Teletha "Tessa" Testarossa's case, it was Submarine technology. She solved Einstein's equations of General Relativity at age 6, designed the super-submarine Tuatha-De-Danaan at age 13 and became its captain upon its completion 2 years later. Being a teenage in charge of a $5 billion secret weapon and its crew of over 200 would breed a very serious personality. Such a personality is only one side of her, which is normally seen in military situations. Tessa is actually a Dojikko and can be helplessly light-hearted outside of work. Can be a tease, deliberately putting male lead, Sagara Sousuke, in a tight spot (feigning ignorance) as he tries to explain why a beautiful girl came out of his shower (this is how Kaname first met Tessa - while she was delivering some food). It's a rare break from the usual pressures of work afterall - she's been expected to excel at everything and look perfect ever since she was young (and she's still young).
Tessa falls in love with Sousuke after a mission gone awry. At the first opportunity after that mission is over, she privately tells Kaname, the other female lead, that they are now going to wage the War of Love Triangles. Without resorting to her superior rank over Sousuke, Tessa does everything she can to develop their relationship. When she has a chance to go on vacation, she chooses to spend the time as a foreign-exchange transfer student at Kaname's school. While enjoying a civilian's life for several days, she stayed at Sousuke's apartment. She crawls into his bed while everyone's sleeping if she is left unsupervised. She was tricked by Sgt. Kurz (in full military-style briefing) to wear ye traditionale School Swimsuit girls have to wear during compulsory education (middle school and below) for the school swimming lesson. Within the boundary of their aliases, Tessa admits to the class that Sousuke (currently unconscious after 3 days of no sleep and diving into the pool) is her childhood sweetheart. When Sousuke wakes up, he comments "Yes it's true, I have a relationship with Tessa that goes beyond your imaginations" (meaning, his Soldier-Officer relationship) which really gets the girls excited and Kaname pissed~
Recently Sousuke has started to see Tessa as a human instead of an untouchable superior being. It happened after Sousuke was abruptly ordered to end his bodyguard mission and return to the submarine full-time. Sousuke passively proclaimed his dissatisfaction to Tessa which she picked up. She knew it was a painful and unfair order to give, but she had to give it for strategic reasons (namely, the Arbalest being locked exclusively to his brain waves). In the heat of the argument, she broke down and cried in front of him in her office where he'd been summoned. Sousuke started to grasp the idea that Tessa was not infallible, that she had her human weaknesses and pressures. A lot happened in this arc (covered in The Second Raid) which led to Sousuke becoming unreliable for the military operation at hand. Tessa disobeyed direct orders from above and arranged for the Arbalest to be deployed unmanned with hope that Sousuke would pull together and pilot it - she had to argue with her (much older and pessimistic) second-in-command that while she admits she loves him, this is a rational decision based on his past performances. In other words, she trusts him and not just because she's in love with him. At the end of the arc, Sousuke apologizes to her and actually calls her by her name - after he takes leave (it was all he could do to talk casually for a short while, sweat breaking everywhere) Tessa is joyed to the point of spontaneous dancing.
The novels have gone even further than this. The next arc after the events of TSR is "Dancing Very Merry Christmas", featuring a more important development for Tessa.