Tonari no Seki-kun

All Rumi Yokoi wants to do is focus during school, but she is constantly distracted by Toshinari Seki, her neighboring classmate. Paying attention during class is the least of Seki's worries, as he obsesses over intricate setups created using an assortment of items, from an elaborate domino course on his desk to a treacherous war played out with shogi pieces. Yokoi desperately attempts to focus in class, only to be repeatedly sucked into his intriguing eccentricities; however, they always seem to end up with her getting in trouble with their teacher. Fortunately, lessons will never be dull with Seki's antics around!

(Source: MAL Rewrite)