Some songs carry so much weight from where they came from that covering them is a risk in itself. Avid by SawanoHiroyuki[nZk]:mizuki — the haunting ending theme of TV anime 86: Eighty-Six — is exactly that kind of song. It hit hard in 2021 and it hasn’t let up since. So when KOKO (幸祜) uploaded her cover on June 4, 2026, featuring none other than chelly (formerly of EGOIST), the expectations were already sky-high.

They cleared them.

The Original: A Song Built From Grief and Hunger

Avid is the ending theme of the TV anime series 86, sung by mizuki under the [nZk] Project as SawanoHiroyuki[nZk]:mizuki. The composer himself described the narrative and world-view of the story as a great motivation for the composition, noting that the time spent building the sounds with vocalist Mizuki and the musicians was very worthwhile yet short-lived.

The song’s title is everything. Avidity means extreme eagerness or enthusiasm, or the overall strength of binding between an antibody and its antigen — and the song lives in that space between desperate longing and the force of connection. The lyrics spiral through imagery of faint light, violent mazes, silenced hearts, and echoes of something lost — all building toward a chorus that feels like shouting into a sky that keeps changing color. It’s emotionally dense, musically intricate, and genuinely hard to cover well. You need two things: vocal range and emotional conviction. KOKO and chelly have both in abundance.

Two Voices That Were Made for This Song

The pairing here is inspired. KOKO has a clear, adult voice that can reach high notes without sounding strained, and her voice is very well-rounded — capable of singing English as naturally as Japanese. She is described as a virtual rock singer whose beautiful long-tone voice carries a floating, weightless quality — songs that deliver a message from her soul to the world. That floating quality is exactly what Avid needs in its quieter verses — a voice that makes the grief feel like it’s hovering rather than crashing.

Against that, chelly brings something harder-edged and immediately recognisable. She has a soft, unique, and well-balanced voice that has soundtracked some of anime’s most emotionally devastating moments — from Guilty Crown to Psycho-Pass to Kabaneri of the Iron Fortress, EGOIST’s music left a mark on an entire era of anime fandom. EGOIST ceased activities in October 2023, making chelly’s appearances in projects like this all the more significant for fans who grew up with her voice.

The vocal split across the cover is handled with real care. The two voices trade lead lines and harmonies in a way that feels deliberate and intimate — KOKO carrying the more inward, searching passages while chelly takes the moments that demand presence and force. When they stack together in the final choruses, the effect is genuinely spine-tingling. This is not two singers performing in parallel. They’re actually listening to each other.

The Production: Clean, Respectful, and Beautifully Executed

Instrumental arrangement by Iwase Ryosuke treats the original with the respect it deserves — this isn’t a reimagining or a stylistic departure, it’s a faithful interpretation that prioritises the song’s emotional architecture while giving it fresh breath. The arrangement retains Avid‘s signature tension — that restless 6/8 undercurrent, the way the chorus seems to open up from below rather than above — without simply copying the original note for note.

Mix by Yokohata Tokuya keeps things spacious and clean throughout, ensuring neither voice gets buried at any point in what is a genuinely demanding arrangement to balance. Illustration by Okusora Keita and video direction by LAKU give the visual presentation an understated elegance that suits the gravity of the material without overshadowing it.

This is listed as cover number No.102 on KOKO’s channel — and signed off with a quietly confident “TO BE CONTINUED.” At this rate, whatever comes next has a very high bar to clear.

Why This Cover Matters

Covers of iconic anime songs live and die by whether they bring something genuine to the source material. A technically proficient but emotionally hollow version of Avid would have been worse than no cover at all. What KOKO and chelly deliver instead is a version that honours the original completely while adding something that could only come from these two specific voices on this specific day.

KOKO debuted on October 25, 2020 under KAMITSUBAKI STUDIO — a label that has consistently produced some of the most thoughtful and emotionally resonant virtual singer content on the internet. This cover is a reminder of exactly why that reputation holds.

If you loved Avid when it first came out, this cover is going to hit you all over again. And if you’ve somehow never heard it — start here, then go back to the original. You won’t regret either listen.

Track Credits

• Title: Avid (cover)
• Original by: SawanoHiroyuki[nZk]:mizuki (86: Eighty-Six ED Theme)
• Cover Vocals: KOKO (幸祜) × chelly (Ex.EGOIST)
• Instrumental: Iwase Ryosuke (岩瀬良介)
• Mix: Yokohata Tokuya (ヨコハタトクヤ)
• Illustration: Okusora Keita (オクソラケイタ)
• Video: LAKU
• Released: June 4, 2026
• Channel: 幸祜 — KOKO — (KAMITSUBAKI STUDIO)

▶ Watch: KOKO × chelly — Avid (Cover) on YouTube