My Neighbor Seki 1 by Takuma Morishige

Toshinari Seki takes goofing off to new heights. Every day, on or around his school desk, he masterfully creates his own little worlds of wonder, often hidden to most of his classmates. Unfortunately for Rumi Yokoi, his neighbor at the back of their homeroom, his many games, dioramas, and projects are often way too interesting to ignore; even when they are hurting her grades.