Leakers unanimously agree that Navia will be a 5-star Nham element DPS character, but whether she'll play infield or outfield is still up for debate. According to Mytour, this depends on the stats that miHoYo will assign to her two skills, as well as their duration. miHoYo still has about three weeks to decide (before starting the 4.3 test) and then another 6 weeks before she officially debuts, so you should only consider the information below and not rush to believe it 100%.

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According to leakers, Navia's elemental skill will transform her umbrella into a gun, continuously firing at enemies while automatically absorbing nearby Crystals. Depending on the type of Crystal, Navia will receive different buffs. This is likely to be Navia's main source of damage. Navia's ultimate skill will create a cannon capable of existing on the field and dealing damage even when the character leaves the field, similar to Yae Miko. It also supports Crystal creation and extends their duration when collected.
Navia's normal attack seems to be overlooked - perhaps because it's not yet complete or not noteworthy. If you want to pre-farm artifacts for Navia based on this information, be cautious. Mytour is confident that miHoYo will release two new artifact sets in version 4.3, and there's a leak that one of them will be for our blonde-haired lady.

Some additional details about Navia's skill set indicate that this character will also possess the ability to self-transform to adapt to the general mechanism of Fontaine characters. Her 'control' weapon will be a heavy sword with high base attack stats and critical damage sub-stats. It sounds quite promising, but we still need more information about its effects.
In general, based on the aforementioned information, Navia would prefer to have Furina on her team to benefit from the incredibly strong Nham damage buff from the Hydro Archon. Meanwhile, leakers also suggest that Chiori, a 5-star character from Inazuma rumored to debut in patch 4.5, would be a more suitable teammate for Navia (compared to Albedo). Let's wait and see if miHoYo decides to 'pivot' or not!
Read more: 3 things you should prepare for Hydro Archon Furina right away