Avant Heim (アヴァント・ヘイム, Avanto Heimu) is the location where the Flügels reside. Regarded as the largest library in Disboard, it is a city floating in the sky, but simultaneously, it is also one of the Phantasma, a sentient being form a part of the Exceed. While changed a floating island after the begin of Ten Pledges, it can transform to a menacing flying fortress armed with numerous cannons capable to unleash destructive barrages.
Avant Heim's structure is made of a huge number of cubes stacked up in a complex and irregular way, making navigation difficult. It also has no roads, as Flügels can simply fly or teleport themselves. Stephanie Dola realizes the city has the poorest accessible environment compared to the technologically-supported Eastern Union and even lesser than the Elchea Kingdom. It is decorated with a skull of a Dragonia with a ribbon on it. This is the skull of the Dragonia that Jibril killed by herself.
Avant Heim was a former protege of the Old Deus Artosh. Along with the Flügel, he aided the god of war into nearly seizing the throne of the One True God. However, it was never accomplished as Artosh was slain before they could capture their prize. He could not accept his master's death and has since been attempting to reach The Red Moon where the Lunamana reside due to the presence of an Old Deus there which he mistakens as Artosh. Avant Heim does not simply float, but "swims" on the spiritual lines of Disboard (which is why he can't ever reach the moon). Avant Heim weeps whenever The Red Moon shines full, and draws near a location where he feels the presence of an Old Deus, hoping one day he can be reunited with his master.
- Avant Heim could translates into 'First Home', with 'Avant' as 'first' in Romansch, and 'Heim' as 'home' in German.
- However, the author has tweeted that 'Avant' comes from modifying the pronunciation of 'abandoned'.
- Kuhaku soon refered Avant Heim as Laputa, a floating castle written by famous animator Hayao Miyazaki.