  Recently, it was pointed out that the electron and muon g-2 discrepancies can
be explained simultaneously by a flavor-violating axion-like particle (ALP). We
show that the parameter regions favored by the muon g-2 are already excluded by
the muonium-antimuonium oscillation bound. In contrast, those for the electron
g-2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We
propose to search for a signature of the same-sign and same-flavor lepton pairs
and the forward-backward muon asymmetry to test the model at the Belle II
experiment.
