Eulrlega.cs

public static class Utility {
    public static bool Eulrlega(string word) {
        var last = word[word.Length - 1];

        if (last < 0xAC00)
            return true;

        last -= (char)0xAC00;

        var jong = (char)((last % 28) + 0x11a7);

        return (jong != 4519);
    }

    public static string GetEulrl(this string word) {
        return Eulrlega(word) ? "을" : "를";
    }

    public static string GetEga(this string word) {
        return Eulrlega(word) ? "이" : "가";
    }

    public static string GetEunnn(this string word) {
        return Eulrlega(word) ? "은" : "는";
    }
}

Usage:

        string itemName;

        itemName = "엘릭서";
        string.Format("{0}{1} 만드는데 필요한...", itemName, itemName.GetEulrl());
        Console.WriteLine("{0}{1} 만드는데 필요한...", itemName, itemName.GetEulrl());

        itemName = "포션";
        string.Format("{0}{1} 만드는데 필요한...", itemName, itemName.GetEulrl());
        Console.WriteLine("{0}{1} 만드는데 필요한...", itemName, itemName.GetEulrl());