The T2K long-baseline neutrino experiment in Japan harnesses its sensitivity to search for CP violation in the neutrino sector by observing the appearance of electron (anti-)neutrinos from a beam of muon (anti-)neutrinos at its far detector, Super-Kamiokande (SK). For the next iteration of T2K's oscillation analysis, a new $\nu_{e}$ appearance sample was developed, targeting charged-current single pion production. This neutrino interaction produces an event with more than one Cherenkov ring at SK, specifically a visible $e$-like and a $\pi^{+}$-like ring. This sample increases T2K's total $\nu_{e}$ CC statistics by $\sim$6\%, paving the way to improving its $\delta_{CP}$ measurements. Additionally, multiple changes were implemented in the estimation of the SK detector's systematic uncertainties. The results from these studies are discussed.