Laminaria japonica, a perennial large brown alga of both medicinal and culinary value, thrives in cold marine environments. As a principal economic seaweed species in China, it is characterized by high productivity and exceptional nutritional density, containing an array of bioactive constituents such as polysaccharides, polyphenols, alginates, and mannitol. These compounds demonstrate diverse physiological activities—including antioxidant, anticoagulant, antiviral, immunomodulatory, and renoprotective effects—enabling extensive utilization of Laminaria japonica across the food, nutraceutical, and cosmetic industries. However, the characteristic marine odor significantly compromises consumer sensory acceptance, presenting a major constraint to the value-added processing and industrial exploitation of Laminaria japonica-based products. Consequently, investigating efficient deodorization techniques and underlying mechanisms is of considerable importance. The primary odorants in Laminaria japonica are predominantly ketones, aldehydes, and alcohols. These volatile compounds can be effectively separated, identified, and quantified through analytical techniques such as Gas Chromatography-Ion Mobility Spectrometry (GC-IMS).Gas Chromatography-Ion Mobility Spectrometry (GC-IMS) integrates the superior separation capability of Gas Chromatography (GC) with the rapid detection characteristics of Ion Mobility Spectrometry (IMS). This combined technique offers high sensitivity, operational simplicity, cost-effectiveness, and requires minimal sample preparation, making it extensively applicable in the analysis and identification of food flavor compounds. Current deodorization methods for Laminaria japonica primarily encompass physical, chemical, and biological approaches. Physical methods, such as masking, adsorption, and encapsulation, do not alter the chemical structure of odor compounds but merely conceal or trap them, resulting in limited deodorization efficiency. Chemical methods, including acid-base treatments or antioxidant immersion, achieve deodorization by facilitating chemical reactions between reagents and odor compounds. Although effective, these methods often introduce chemical residues that are challenging to eliminate, posing potential risks to food safety. Biological deodorization represents an environmentally friendly, mild, and efficient approach that utilizes microbial metabolism to convert odorous substances in Laminaria japonica into non-odorous macromolecules. This method not only effectively eliminates undesirable odors but also enhances the overall flavor profile of the final product. However, most existing biological deodorization processes utilize Laminaria japonica pulp or fragments as raw materials, which impedes subsequent refined processing. To address this limitation, this study employs whole Laminaria japonica blades for microbial fermentation-based deodorization, aiming to establish a superior raw material foundation for downstream processing. To investigate the sources of off-odors in salted Laminaria japonica and the regulatory effects of yeast fermentation on its flavor profile, this study utilized intact salted Laminaria japonica (without comminution) as the raw material. Three yeast strains—Pichia kluyveri CICC 32844, Saccharomyces cerevisiae CICC 32883, and Wickerhamomyces anomalus CICC 33313—were selected for fermentative deodorization of both raw and cooked salted Laminaria japonica. Sensory evaluation results indicated minimal and non-significant differences in texture and color among samples fermented with the three strains. However, significant variations in deodorization efficacy were observed. Wickerhamomyces anomalus demonstrated the highest deodorization efficiency and overall performance for raw salted Laminaria japonica, whereas Saccharomyces cerevisiae exhibited optimal deodorization and comprehensive effects for cooked salted Laminaria japonica. Consequently, W. anomalus and S. cerevisiae were identified as the most suitable strains for raw and cooked salted Laminaria japonica, respectively. These two selected strains were employed for flavoring and fermenting the salted Laminaria japonica. The volatile flavor compounds in samples subjected to different treatment conditions were qualitatively and quantitatively analyzed using Gas Chromatography-Ion Mobility Spectrometry (GC-IMS), enabling the characterization of flavor profile alterations and comparison with commercial Laminaria japonica products. The Relative Odor Activity Value (ROAV) method was applied to comprehensively evaluate the flavor characteristics and identify key compounds across different sample groups. Results revealed that the off-odors in salted Laminaria japonica were predominantly attributed to aldehydes and ketones. Among these, 1-octen-3-one was identified as the most potent odor marker, whose mushroom and earthy notes contributed more significantly to the characteristic marine odor than traditionally recognized aldehydes such as (E)-2-nonenal and propanal. While thermal processing could generate pyrazine flavor compounds like 2,3,5-trimethylpyrazine via Maillard reaction, their actual flavor contribution remained minimal (ROAV < 0.1), demonstrating limited masking effects. After fermentative flavoring, the sensory quality of salted Laminaria japonica was significantly improved. In raw salted Laminaria japonica, the process generated compounds such as isovaleraldehyde and propyl acetate, which synergistically masked the off-odors. In cooked salted Laminaria japonica, the fermentative flavoring produced isovaleraldehyde and alcohols including n-hexanol, which effectively concealed the marine odor while increasing the diversity of aroma compounds. A comparative flavor analysis between the experimental samples and commercial products identified isovaleraldehyde, phenylacetaldehyde, p-methylbenzaldehyde, 1-octen-3-one, acetylpyrazine, and diallyl disulfide as key flavor compounds common to all samples. Among these, isovaleraldehyde imparted a distinct chocolate and fatty aroma to the Laminaria japonica samples, contributing significantly to the overall flavor profile. Notably, significant differences in the overall flavor composition were observed between the experimental and commercial samples. Following the fermentative flavoring treatment, 1-octen-3-one was no longer the dominant contributor to the flavor profile, demonstrating the feasibility and effectiveness of the fermentation-based flavor modulation process developed in this study. This study conducted qualitative and quantitative analyses of key flavor compounds in raw salted Laminaria japonica and its seasoned/fermentatively flavored derivatives. By systematically investigating the compositional differences and dynamic changes in volatile profiles before and after yeast-mediated fermentation, and through comparative analysis with commercial products, we successfully developed Laminaria japonica products with distinctive flavor characteristics. The research provides a theoretical foundation for microbial fermentation-based flavor regulation in seaweed processing, reveals the dynamic transformation of flavor compounds during microbial fermentation, and offers novel strategic insights for the development of seaweed products and optimization of microbial deodorization technologies.