Undertown manga volume 2 — Jim Pascoe

The second book in a manga adventure series about a young boy who travels through a portal in his bedroom to find a powerful healing artifact.
 
On a quest to find a magical object to save his sick father, young Sama journeys through the dark world of Undertown. But will Sama find the Sugar Stone, or will the Cloud prevent him from finding what his father needs? The Undertown saga continues.
 
Praise for Undertown #1:
 
“This fantasy manga presents the right mix of familiar tropes along with new ideas that should capture the imaginations of more than a few readers.” -- Publishers Weekly