Doutei Saizensen

From Fantasyshrine:

Even after Colonel Michel Rosenberg and Hans Schuyler had their honeymoon, their life together was still filled with H-action! This seemed to have affected the Defense Army as a whole. Love started blooming everywhere: between the enemy commander and the colonel?s assistant, Miller; the instructor and his new soldier; the intelligence captain and the enemy?s spy; the mercenary captain and the elite chief of staff. Couples were accumulating in droves!

Reference made to 'Koutetsu no Daitenshi'.
Colonel Rosenberg and Hans story starts in 'Koutetsu no Daitenshi' and then continues in 'Datenshi ni Sasageru Uta'

Chapter 1: C'mon Baby, To My Army! ~ Pgs. 8-38
Colonel Rosenberg threw away Millers Ring, This time it*s unforgiveble, Miller runs off but gets caught by the enemies. Colonel Kingstones chance has come to conquer Millers heart.

Chapter 2: The Waterside Lovers ~ Pgs. 40- 54
A very hot Day, colonel rosenberg is just melting away under the heat, then hans to go swimmeing in a near by creak...

Chapter 3: The Rebel

Chapter 4: My Beloved Exile

Chapter 5: First Line of Virginity ~ Pgs. 2-33

Chapter 6: The Beast Who Whispers Love
A pretty elite officer gets kidnapped by an ultra manly mercenary, and he would do anything ( including H stuff) to get back to headquarters!

Chapter 7: Captin Bennett's Diary ~ Pgs. 35-39