
Quick answer — True performed 3 anime themes, including "Another colony" from That Time I Got Reincarnated as a Slime, "Storyteller" from That Time I Got Reincarnated as a Slime Season 2, "Divine Spell" from Regalia: The Three Sacred Stars.
True performed the anime theme songs "Another colony" (That Time I Got Reincarnated as a Slime), "Storyteller" (That Time I Got Reincarnated as a Slime Season 2), "Divine Spell" (Regalia: The Three Sacred Stars).
True's first listed anime theme is "Another colony", the ending of That Time I Got Reincarnated as a Slime.