CIX Begin a New Chapter with 'THUNDER FEVER' as a Four-Member Group

CIX released their seventh extended play THUNDER FEVER on January 23, 2025 — their first as a four-member group following Bae Jin-young's departure in August 2024. The release marked one of the more significant transitions in recent third-generation K-pop: a group moving forward with a reconfigured lineup while maintaining enough identity continuity to signal that the project was defined by its direction, not only by its personnel.

The title track "THUNDER" is an electronic pop release built on dynamic rhythmic shifts and a high-energy dance break, using the metaphor of thunder and lightning to frame confused emotional states in the context of romantic intensity. Stylistically, it positions CIX within the new-gen funk-pop and electronic dance lineage that groups like RIIZE had been developing in the previous year.

Debut, Identity, and the Cost of a Departure

CIX — Complete in X — debuted on July 23, 2019 under C9 Entertainment with the EP Hello, Strange Place. The group launched as a five-member act: BX, Seunghun, Bae Jin-young, Yonghee, and Hyunsuk. From the beginning, Bae Jin-young — a former member of Wanna One, the survival show group that had defined 2017-2018 K-pop's peak idol-competition era — brought an existing audience to CIX that predated the group's debut. His presence anchored the group's early commercial profile in ways that the other members were still building toward.

C9 Entertainment announced on August 5, 2024 that Bae Jin-young's exclusive contract had concluded on August 1 and would not be renewed. He subsequently signed with AURA Entertainment in December 2024 and announced a solo debut for 2025. The timeline was clean: a contractual separation, not a conflict. But it removed the group's most recognizable name from the lineup at a moment when K-pop's fourth-generation acts were establishing the competitive landscape that would shape the next three years.

The question facing the remaining four members — BX, Seunghun, Yonghee, Hyunsuk — was one that faces every partially-restructured group: whether the reconfigured lineup would be treated as a continuation or as a de facto relaunch. CIX and C9 chose continuation. THUNDER FEVER did not announce itself as a reset; it announced itself as a seventh EP.

The Album as Structural Argument

The five-track structure of THUNDER FEVER reflects a strategic distribution of new and familiar material. Three new tracks — "Bad Moves," "THUNDER," and "My Everlasting Sun" — appear alongside new versions of previously released songs "Lovers or Enemies" and "그림자 (My name is shadow)." The inclusion of two revised earlier tracks serves a dual purpose: it provides sonic continuity with the pre-departure catalog while signaling that the existing material remains relevant to the current group identity.

The physical release in six editions — Thunder, Fever, and four individual Keyring versions — extended the standard idol album fan-engagement strategy into the new lineup configuration. Individual member versions create separate collection points for each of the four remaining members, a mechanism that generates parallel fan investments while reinforcing the group as a collection of distinct individuals rather than an anonymous collective.

Critically, "THUNDER" itself received attention that went beyond the transitional narrative. Reviews noted the track's alignment with the new-gen electronic pop direction, with some outlets describing it as CIX's most competitive release to date — an assessment that, if accurate, suggested the four-member configuration had not simply maintained but potentially improved the group's sonic positioning.

What Member Departures Do to Group Continuity

Bae Jin-young's departure from CIX is not exceptional in K-pop's structural history, but the specific circumstances — a major-label survival show alumnus with a pre-existing individual fanbase, leaving a mid-tier group at the beginning of an era he helped establish — makes it a useful case study in how groups absorb membership changes.

The contrast with groups that have dissolved after member departures versus those that have continued is instructive. INFINITE continued after Hoya's departure in 2017; BEAST became Highlight after a restructuring in 2017; HIGHLIGHT continued and released new music through 2024. In each case, the group's decision to continue rested on whether the remaining members had sufficient collective identity and audience to sustain commercial activity. For CIX, the answer the THUNDER FEVER release provided was: yes, and the music supports it.

Impact and Reception

The fanbase response to THUNDER FEVER reflected the mixed emotions common to major lineup changes. Some FIX (the group's fandom) expressed continued support for the four remaining members; others were navigating the transition of their individual investment in Bae Jin-young toward his upcoming solo work. These parallel trajectories — continued group fandom and transferred individual fan interest — are common in post-departure scenarios, and in most cases do not mutually exclude each other. Fans of a group and fans of a departed member can sustain separate but simultaneous interests.

The album's commercial performance did not reach the heights of CIX's earlier major releases, but it provided a baseline that confirmed continued viability. The electronic pop direction of "THUNDER" gave the group a clear sonic footprint for the post-departure era — a direction differentiated enough from their earlier material to register as a fresh start rather than a reduced continuation.

Future Outlook

CIX's transition to a four-member lineup with THUNDER FEVER established the parameters for what the group would be in 2025 and beyond. The remaining four members — each building individual identities within the group frame — had a clean starting point in the January 23 release. In the months that followed, the group would continue to release new material and engage their audience across platforms, demonstrating that the transition, while significant, had not interrupted the project's forward motion. The departure of a prominent member tests whether a group exists as a vehicle for individual star power or as a collective with its own cultural weight. THUNDER FEVER submitted CIX's answer to that test.