Mika's primary utility comes from his Elemental Skill's Attack Speed boost, so his natural stats are irrelevant. You may however give him weapons that enhance his ability to heal on your team.
Mika's Elemental Burst reduces his Max HP. So weapons that increase his HP will allow him to heal more per Normal Attack. However, his Burst is a little expensive for the amount of Energy he generates, which means Energy Recharge weapons are also useful.
Mika should belong with his DPS Polearm characters because he gets a 40% damage bonus against Slimes.
Starglitter, a prototype, is now available.
Mika's Burst is a great F2P option because it's a simple trick to craft in-game. After using an Elemental Skill, Mika's stat stick increases.
The Catch is a good F2P polearm to have while fishing, due to its passive focus on Elemental Burst DMG rather than Normal and Charged Attacks. It boosts his Elemental Burst DMG by 16% and Crit Rate by 6%, like t he Prototype Starglitter.
Lance of Favonius
Favonius Lance's main skill is Energy Recharge, although it's significantly lower. However, at R5, Mika can be run with a character who has better Cryo application to benefit from Superconduct.
Favonius Lance has a drawback: a large number of characters would want to use it. Yun Jin, for example, is a character who would appreciate having Favonius Lance. It is also only available in the gacha, unlike Prototype Starglitter and The Catch.
Genshin Impact is readily available on PS4, PS5, Windows PC, and mobile devices. Mika is a 4-star guy, which means he's always in the loop.