In Another World With My Smartphone

In Another World with My Smartphone (original title: Isekai wa Smartphone to Tomo ni) is a classic isekai anime where the protagonist gets a laid-back, overpowered second life in a fantasy world.

Quick synopsis: 15-year-old Touya Mochizuki is accidentally killed by God (via a lightning mishap). As an apology, God reincarnates him into a magical fantasy world and grants him a wish. Touya simply asks to keep his smartphone—which God upgrades so it works there (recharges with magic, has GPS for the new world, internet access to Earth's web, etc.). Touya also gets boosted abilities, like high affinity for all magic types, making him ridiculously powerful and versatile.

In the new world, Touya adventures casually: he takes on guild quests, makes friends (mostly cute girls who end up in his growing harem), solves problems for kingdoms, travels freely, and uses his phone for everything from navigation and research to introducing Earth concepts like food or tech hacks. It's very much a relaxed, slice-of-adventure story with harem elements, comedy, light action, and no real high-stakes drama—more about him living an easy, wish-fulfillment life while building relationships and a bit of a nation/legacy along the way.

It's a chill, fun power-fantasy isekai if you're into that vibe!