My idea is this:
After that John came to earth, a little didactic survived, rescuing Cortana to John she said: Most of me is down there, then they were remnants of it along with the remains of the composer, the training DIDACT to notice this takes what little remained of cortana and repair on a HALO (REQUIEM was destroyed in SPARTAN OPS.)
To compensate for cortana the programno use against humanity, so having all the information about humanity (since this made cortana basae HALSEY's mind, the smartest human who ever lived)
and would have everything you need to plan your revenge.
Causing UNSC and JOHN and have to face with the DIDACT and the new CORTANA
If this badly translated, sorry is with google
If you want to translate it yourself here's how I wrote
Mi idea es esta:
Despues de que John llegara a la tierra, un poco de didacta sobrevivio, Cortana al rescatar a John ella dijo: La mayor parte de mi esta ahi abajo, entonces estaban restos de ella junto con los restos del compositor, el didacta al notar esto toma lo poco que quedaba de cortana y la reparo en un HALO ya que REQUIEM fue destruido en SPARTAN OPS.
Al reparar a cortana la programno para usarla en contra de la humanidad, asi teniendo toda la informacion sobre la humanidad (ya que cortana esta hecha a base de la mente de HALSEY, la humana mas inteligente que haya existido)
y tendria todo lo necesario para planear su venganza.
Causando que JOHN y la UNSC se tengan que enfrentar a didacta junto con la nueva CORTANA
Thanks for reading my idea, Greetings
