Every time people bring up that Mahouka thing I keep thinking it's some sort of elaborate prank or in-joke with all the participants unusually disciplined to keep the charade going.
Mahouka: The Mornington Crescent of bad anime.
"I really liked how in Season 7 he oscillated the oscillations around a Quas-Tertertianary Matrix to stabilize the Parallaxing Non-Convergiances in order to annihilate an alien civilization for calling his sister's brownies 'okay.'"
"Season 8 where he had to sharpen a pencil had way more drama, you could really feel the struggle and determination."
It kind of hits a certain weirdness in terms of what is usually "Super appealing characters" which is... they are a LOT more interesting to chase then they would be in a relationship.
Do you honestly think Tetsuya would be particularly warm, caring, or thoughtful? Mind you I am sure if it happened that he would buy her but a single rose which would cause her panties to vaporize on the spot... But seriously. (Heck I am sure in bed Tetsuya somehow memorized the Kama Sutra and has perfected it... in spite that being against his character... because he is a Mary... err I mean because he is such an erudite)
Trust me lady, you chose the right guy.
Given that he's openly (and bullshittingly) described as having exactly one emotion, that being love for his sister, I would assume any kind of relationship with Tatsuya would basically amount to being a doll for his sister.
"Oh Tatsuya-sempai, what did I ever do to deserve you?!"
"My sister picked you out of a lineup because she thought it'd be cute if I got married. So I did."
"Wow, I'm so lucky!!! So, you wanna, I dunno, interact with me in any way whatsoever?"
"No. Unless my sister says so. Also if you displease her in any way I'll vaporize you for her on the spot."
So basically a loveless hell with a cold monster.
...man, Tatsuya really would make an excellent villain.