  We construct a weakly-coupled renormalizable model to explain the
$750\mbox{GeV}$ diphoton excess. The $750\mbox{GeV}$ resonance (denoted as
$X(750)$) is interpreted as a pseudoscalar coming from a complex singlet. The
model also naturally provides a dark matter candidate. One most attractive
feature of the model is that decays of $X(750)$ are all loop-induced so the
diphoton rate is not diluted by unwanted tree level branching fractions.
Relevant Yukawa interactions need not to be tuned to near non-perturbative
region to explain the rate. The model is highly predictive, including the
pseudoscalar nature of $X(750)$, and two nearly mass-degenerate exotic quarks
carrying electric charge $5/3$ and $2/3$, respectively. Rich phenomenology is
expected with respect to collider searches, flavor physics and dark matter
detection, if $X(750)$ can be pinned down by future LHC experiments.
