[Fuugetsu Makoto] Kakusansei Million Arthur - Chapter 14 [2014][AP]

[Shadow00000]

[Fuugetsu Makoto(楓月誠)] Kakusansei Million Arthur - Gunjou no Shugosha (拡散性ミリオンアーサー ―群青の守護者―) - Chapter 19 [2015]

Serialization:

Dengeki Daioh (電撃大王)

http://katfile.com/ruo039zztyc1.html

Based on the 2012 card game published by Square-Enix. Bisclavret was previously killed or heavily injured by the very same foe she faces now, I think since she got cocky the first time she decided to not risk it again and fuses right away even if her power is greater now. One of the panels shows the flashback.