A side story of Maiden Rose - a peek into Taki and Claus' time spent together back in their dorm room at Luckenwalde.

Originally published as a doujinshi in 2005 under the title Maiden Rose, with "Luckenwalde no Heya de" acting as a secondary title on the first page inside the cover; it's a copy-bon sketch version that was later shaded and expanded to be properly printed and bound in 2009 under the title Hyakujitsu no Bara Maiden Rose.
The 2005 version has some sketches and comments at the end that aren't included in the later version.

Chronological order of the Luckenwalde no Heya de series:

1. Luckenwalde no Heya de

2. Luckenwalde no Heya de II:
   Chibi Taki has a fever.
   (Originally published in Maiden Rose Vol.2 Release Commemorative Booklet)

3. Luckenwalde no Heya de III:
   Klaus shares his sister's honey. Taki likes sweets.
   (Originally published as a separate doujinshi entitled Jingi naki Nikukyuu Paper - Amaimono wa Betsubara Hen)

4. Luckenwalde no Heya de IV:
   Klaus is a crappy spy.
   (Originally published as a separate doujinshi entitled Jingi Naki Nikukyuu Hen - Shuumatsu no Sugoshikata)

5. Luckenwalde no Heya de V:
   Taki gets a present from Klaus's sister.
   (Originally published as a separate doujinshi entitled Maiden Rose (2009))

6. Wheel of Fortune
   Back in Luckenwalde, Klaus and Taki are mourning the death of some of their companions. They go to their usual inn, and Taki meets a mysterious stranger.
   (Later reprinted in volume 2 of Re:Collection)

7. Rosa Alba I
   A new arc in the Luckenwalde era storyline, set after 'Promise' and before 'Wheel of Fortune'. An old friend comes back from the past to see Klaus...But is the visit what it seems? And how will it affect Taki?
   (Later reprinted in volume 2 of Re:Collection)

8. Rosa Alba II
   The boys go into town with Klaus's old comrade. Taki makes coffee while Klaus reminisces. And Enrico...well, who thinks he has a hidden agenda??

9. Danshou (Fragment)
   Klaus and Taki spend a quiet moment in bed in their room at Luckenwalde. Very short and no dialogue at all, just a little voiceover.

Danshou was later reprinted in Lups et Flos with an extended section that's written from Klaus's viewpoint and connected to 'Rosa Alba' and some other bits in the manga.