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We report that Ly$\alpha$-emitting galaxies (LAEs) may not faithfully tracethe cosmic web of neutral hydrogen (HI), but their distribution is likelybiased depending on the viewing direction. We calculate the cross-correlation(CCF) between galaxies and Ly$\alpha$ forest transmission fluctuations on thenear and far sides of the galaxies separately, for three galaxy samples at$z\sim2$: LAEs, [OIII] emitters (O3Es), and continuum-selected galaxies. Wefind that only LAEs have anisotropic CCFs, with the near side one showing lowersignals up to $r=3-4~h^{-1}$ comoving Mpc. This means that the average HIdensity on the near side of LAEs is lower than that on the far-side by a factorof $2.1$ under the Fluctuating Gunn-Peterson Approximation. Mock LAEs createdby assigning Ly$\alpha$ equivalent width ($EW_\text{Ly$\alpha$}^\text{obs}$)values to O3Es with an empirical relation also show similar, anisotropic CCFsif we use only objects with higher $EW_\text{Ly$\alpha$}^\text{obs}$ than acertain threshold. These results indicate that galaxies on the far side of adense region are more difficult to be detected ("hidden") in Ly$\alpha$ becauseLy$\alpha$ emission toward us is absorbed by dense neutral hydrogen. If thesame region is viewed from a different direction, a different set of LAEs willbe selected as if galaxies are playing hide-and-seek using HI gas. Care isneeded when using LAEs to search for overdensities.

Catch Me if You Can: Biased Distribution of Ly$\alpha$-emitting Galaxies according to the Viewing Direction