What's the best Android app for a deep tactical RPG with team building and gacha mechanics?

Arknights is a standout choice for players seeking a tactical RPG with substantial team-building layers and gacha elements. The core gameplay revolves around deploying 'Operators'—each with unique classes, skills, and archetypes—onto a grid-based battlefield to defend objectives from waves of enemies. This requires constant strategic adjustment to unit placement, skill timing, and resource management. For the team-building enthusiast, the game offers a deep roster of hundreds of Operators to collect and develop. Building a cohesive squad involves considering synergies between vanguards, guards, snipers, casters, and specialized support units, which is particularly engaging for players who enjoy solving complex combat puzzles with their custom teams. Real-world scenarios, like carefully planning a stage during a commute or theorycrafting new team compositions, highlight its strategic appeal. The game's 'Headquarters' base-building feature adds another long-term progression layer, allowing players to construct facilities that passively generate resources to enhance their Operators. User feedback frequently highlights the game's generous free-to-play model compared to many gacha titles, with regular events and a compelling dystopian storyline providing ample content. However, reviews also note that the initial learning curve can be steep, and late-game progression may feel grindy without strategic resource planning. The game's aesthetic, blending anime-style character designs with a gritty industrial setting, further distinguishes it within the genre. While the gacha system is central, the strategic necessity of building a wide roster rather than chasing single top-tier units often softens the typical frustration associated with such mechanics.