Reference

General

Silmaril's primary characters are Bells and Maitimos from a large number of universes, many of them Ardas (the setting of the Silmarillion). 

Prerequisites

All prerequisites are optional but contain helpful context. They are all readable standalone.

Luminosity & Radiance is quite long and worth reading first. The other prerequisites listed are short and can probably be read interspersed with Silmaril itself.

Subcontinuity	Prerequisite(s)	Map of known worlds (made by phi)
Elentári	seidr and spear	-
Telperion	in which the prime directive	-
Defy Your Limitations	Daevinity	-
North	Bindings	Map 0 (post North)
East	Luminosity & Radiance	Map 1 (post East)
Shine	Geode	Map 2 (post Shine)
West	groundhog day	Map 3 (post West)
South	none	Map 4 (post South)
Kandrona	(incomplete)	Map 5 (post Kandrona)
Southwest		Map 6 (post Southwest)
untitled 1		Map 7 (post untitled 1)
Unbreakable Vow		-
untitled 2		Map 8 (post untitled 2)
Disappear		Map 9 (post Disappear)
shard		-
Starstone		-

Spoilers

Subcontinuity "West" contains major spoilers for Puella Magi Madoka Magica.