[m]Only remember 2 details such as:

1. He has a female classmate who he has at school before leaving for the frontline to help the female knights. [spoiler] This classmate crossdresses to become his sort of guard/butler, hiding her true identity from him.

2. about 20 chapters in he meets two prisoners the knights have, which tries to get answers from before saving one of them.

Any help is appreciated
Thanks

Sounds like Hagure Seireii no Shinsatsu Kiroku - Seijo Kishidan to Iyashi no Kamiwaza
Edit: Or not. Missed the part about the crossdressing.
Edit 2: Nervermind. Actually re-read a couple of chapters and found the crossdressing guard/butler...

~4400 manga completed
~1700 ongoing...

Thank you very much mate.