Fate/Grand Order

The Fate/stay night series is one of the most popular franchises in Japan, and its mobile phone adaptation - Fate/Grand Order is a solid take on the gacha RPG genre that provides an excellent introduction to the mythology. That mythology plays well to the fundamentals of the genre as well. You play a Master, who can summon various followers known as "servants" throughout history.

In practice, that means that you're building a small army that draws liberally from history, literature, and mythology from around the world. The biggest draw of the game arguably isn't about combat at all but rather collecting and empowering these characters. Unfortunately, who you collect is largely left to luck of the draw, but Fate/Grand Order is relatively generous with its currency.

The combat takes an interesting twist on typical gacha RPGs too. Characters are split into three categories, and rather than fighting directly using menus, players draw cards. Since these cards are associated with different characters and actions, there's a whole lot of room to create a tactical style that matches you and your team. The result is one of the most interesting gacha games around, although the vast cast of characters and interlocking systems may be intimidating to new players.