Tensei Shitara Slime Datta Ken: Bangai-hen - Toaru Kyuuka no Sugoshikata

Rimuru and his friends go to the "Magic Tower", a place where magic from all over the world gathers to develop new special moves, and they are supposed to be busy with their research, but they get caught up in a conflict...
(Source: Official Website, translated)
Notes:
- Chapter 0 is included in the total chapter count.
- Adapted from a new webnovel written by Fuse in celebration of the 10th anniversary of Tensura.
- The story takes place between volumes 9 and 10 of the LN.