Rhiannon is a 6-star Beast Afflatus Mental Support introduced in Reverse: 1999 Version 3.7. What makes her unusual is not raw damage, but how many teams she can strengthen at once. Her Universal Fit mechanic allows her to count as a member of Lingering Glow, Bloodtithe, Dynamo, Impromptu, and Instrument archetypes, while her kit brings Incantation Might, Ultimate Might, Critical DEF reduction, teamwide DMG Bonus, and even extra action rounds. That combination makes Rhiannon one of the most flexible support options for accounts built around several different archetypes.

This Rhiannon build guide covers Rhiannon best builds, Arcane Skills, Resonance, Portraits, team options, gameplay, and pull advice.

Building a new 6-star all the way to Insight III and a usable Resonance level also means another round of resource farming. If you maintain multiple Reverse: 1999 accounts, OSLink's multi-instance and automation features can help run repetitive resource stages across several PC emulator sessions, reducing the amount of manual farming needed while preparing Rhiannon and her teammates.

r1999 Rhiannon Overview

Rhiannon's biggest advantage is flexibility. Universal Fit makes her count as Lingering Glow, Bloodtithe, Dynamo, Impromptu, and Instrument, allowing her to interact with effects that check for those archetype members. It does not mean she automatically generates every archetype's unique resources, but it lets her occupy support slots that would normally be much more restrictive.

Her Insight III is also a major reason to finish building Rhiannon early. At battle entry, she gains 3 Moxie and fills Raptor Kinship by 70%. At the end of a round, she can consume Attunement to gain another Moxie, greatly accelerating her first Ultimate.

Rhiannon Arcane Skill Breakdown

The Rhiannon arcane skill set becomes significantly stronger after her Ultimate activates Aegis. Before that point, she is already a team buffer; afterward, her own Incantations become much less demanding on the team's AP economy.

Babble-Gabble

At Rank 1, Babble-Gabble deals 200% Mental DMG to all enemies. Before attacking, it can consume one Attunement stack to raise Rhiannon's ATK for the round.

The more important part appears while Aegis is active. Babble-Gabble then reduces all enemies' Critical DEF by 15%, with additional reduction based on Rapport stacks. This turns an otherwise straightforward AoE Incantation into a useful offensive debuff for Crit-oriented damage dealers.

Sneaky-Peaky

Sneaky-Peaky is arguably her most universally useful regular Incantation. It gives all allies Flocksong for three rounds, providing:

• Incantation Might +30%
• Ultimate Might +30%

While Rhiannon has Aegis, the card additionally gives the team 15% DMG Bonus, with more DMG Bonus added according to her Rapport stacks.

That makes Sneaky-Peaky particularly valuable for damage dealers whose rotation contains both normal Incantations and a powerful Ultimate rather than characters relying almost entirely on one damage source.

Chirping Chorus

Chirping Chorus is the Ultimate that unlocks Rhiannon's stronger gameplay loop.

All other allies receive Adar Llwch Gwin for three rounds, increasing their ATK and Max HP based on Rhiannon's own corresponding stats. Meanwhile, Rhiannon's Incantations gain Aegis for four rounds, and her own Incantations do not require AP to cast while the effect is active.

At P0, Adar Llwch Gwin converts 8% of Rhiannon's ATK and Max HP into additional stats for her allies, up to the skill's listed caps. This is the main reason ATK and Max HP matter more than trying to turn her into a conventional Crit damage dealer.

Raptor Kinship, Rapport, and Sensory Bond

Rhiannon's defining mechanic is Raptor Kinship.

Once Raptor Kinship reaches 100%, she can enter Sensory Bond before Incantations are used. Sensory Bond grants the team an extra round of actions where enemies cannot act, and Feast Call enters the AP Area during that round.

Feast Call deals 1500% Mental DMG to all enemies, gains another 150% Mental DMG for each Rapport stack, and always receives Afflatus Advantage. Rapport itself increases all allies' Afflatus Advantage DMG by 4% per stack at P0, up to five stacks.

This extra-turn mechanic is one of the main reasons Rhiannon remains useful even outside a single dedicated archetype.

Rhiannon Gameplay

The basic Rhiannon gameplay flow looks like this:

Build the first Ultimate → Cast Chirping Chorus → Enter Aegis → Use AP-free Incantations → Build Rapport and Raptor Kinship → Trigger Sensory Bond → Take an extra action round

The first Ultimate is especially important. Once Aegis is active, Rhiannon can play her own cards without consuming the team's normal AP, meaning her buffs and debuffs interfere much less with the main DPS rotation.

During the Aegis window, prioritize Sneaky-Peaky when your DPS is preparing a damage cycle, then use Babble-Gabble to set up Critical DEF reduction when the team benefits from Crit. Meanwhile, consuming Attunement feeds Raptor Kinship and generates Rapport, gradually preparing the next Sensory Bond window.

The important point is that Rhiannon should not steal AP from your carry. Once the first Ultimate is online, she becomes an extremely AP-efficient support.

Rhiannon Best Builds

The safest Rhiannon builds focus on strengthening the stats her support effects actually use.

Build Priority

Insight III > Psychube > Resonance > ATK / Max HP

Best Psychube: The Soft Rain of Yesterday

The Soft Rain of Yesterday is the dedicated Psychube that best matches Rhiannon's kit.

Its effects increase the carrier's ATK and Max HP when used by a Universal Fit character, while actively casting Incantations builds a teamwide DMG Dealt buff. A Beast carrier can also provide additional team Critical DMG after using an Ultimate.

All three components fit Rhiannon naturally: ATK and Max HP improve her Ultimate's team stat conversion, her AP-free Incantations allow frequent active casts, and Chirping Chorus activates the Beast-related Ultimate effect.

For that reason, it is the best dedicated choice when optimizing Rhiannon's build.

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Rhiannon Resonance

Rhiannon resonance should primarily support ATK and Max HP rather than chasing maximum personal Crit stats.

A strong general priority is:

ATK ≈ Max HP > defensive utility > personal offensive stats

Equanimity Resonance Pattern is recommended because it aligns well with her ATK/HP scaling.

The logic is straightforward: raising ATK helps Adar Llwch Gwin's ATK contribution, while raising Max HP improves its HP contribution and makes Rhiannon harder to remove. Her personal AoE damage is useful, but it is not the primary reason she occupies a team slot.

Best Rhiannon Team Compositions

The best part of Rhiannon team building is that she is not locked to one archetype.

Bloodtithe Team

This Bloodtithe lineup currently ranks among the strongest team archetypes. Rhiannon qualifies as Bloodtithe through Universal Fit while bringing extra turns, Flocksong, DMG Bonus, and Critical DEF reduction without heavily competing for AP after her Ultimate.

Conduit Team

The Conduit setup is another excellent Rhiannon team. The Twins need large amounts of Energy, while Coppélia and Everecho help supply the system. Rhiannon contributes differently: after activating Aegis, she can clear her normal Incantations without consuming AP, helping prevent ordinary cards from interfering with Conduit Energy-card flow.

Her Universal Fit trait also means she can function in Dynamo, Impromptu, and Lingering Glow setups when you need a flexible support slot.

Rhiannon Portrait Priority

Rhiannon portrait upgrades are good, but the important point is that P0 already contains her entire core support engine.

Final Thoughts

Rhiannon succeeds because She provides strong Incantation and Ultimate buffs, lowers Critical DEF, grants a teamwide DMG Bonus, boosts team ATK and Max HP, becomes AP-free after activating Aegis, and eventually creates an entirely new action round through Sensory Bond.

The recommended build is straightforward: reach Insight III, use The Soft Rain of Yesterday, build ATK and Max HP through Rhiannon resonance, and stop at P0 unless you specifically want P1's faster opening or P2's stronger extra-turn engine.

She is especially strong alongside Nautika in Bloodtithe teams and The Twins, Coppélia, and Everecho in Conduit teams, but Universal Fit means those are far from her only options.

And while preparing those teams, OSLink can help with multi-instance AFK farming and repetitive resource collection, making it easier to raise Rhiannon and several teammates across multiple accounts without manually handling every farming run.