[Narvi]

Courtesy of Silver001 from Jcafe. It's taken from 4chan.

Spoiler for Spoiler from light novel:

1) Miyuki and Tatsuya ARE siblings. Maya lies to tatsuya and tells him they are not, and that tatsuya is her son. It's a 100% lie

2) the lie is made public, "officially" making them not brother/sister... this is so "tatsuya" can be married to Miyuki without claims of "incest" (though the lie makes them first cousins)

3) Miyuki was not created "for" tatsuya. She was ALTERED. You, you clearly never read this fucking series, but the Yotsuba alter all their fucking Mages. They have a dark reputation because they are the only one of the 10 master families which is believed to still do it. It's not the same as the sakura series. The sakura series are all clones. Miyuki is the flesh and blood sister of tatsuya, however she was altered to allow her to control him.

NOW - do the fucking math

Tatsuya wasn't "created" until he was a 6yo failmage, and they're almost the same age. Miyuki was altered AFTER tatsuya was created to help put some controls onto him.

she's the real deal, she's not some altered generic failure like Leo or the sakura series. she's a world class mage who was altered to add some extra precautions to keep a firm handle on tatsuya.

4) the marriage is to legitimize Miyuki's claim on the head of the household, as she's NOT maya's daughter. by lying and claiming tatsuya is her son, she legitimizes Miyuki's claim. She also wins Miyuki's loyalty because by engaging them, she frees tatsuya from his bondage as a "protector" while at the same time keeping him as a protector

the marriage was just another "scheme" to keep tatsuya locked into the family. Maya is just pulling an Aizen here. And of course since tatsuya was "altered" to only have feelings for his sister he's roped into as if a programmed robot, while Miyuki is too dumb to figure out what's really going on