Kenta Sugai. Grammaticalization of the Verb imam 'have' in Bulgarian: The ima da construction. Studies in Linguistic Sciences. 2024. 1. 94-106
Kenta Sugai. How and what should be included in a Bulgarian textbook for Japanese speakers? An examination in the light of differences between written and spoken language. Българистиката по света. Филологията у дома. Сборник с доклади от международната научна конференция. 12-14 октомври 2023 г. 2023. 16-23
Kenta Sugai. The Future Tense Construction of 'Have' in the Bulgarian Dialect of Băleni-Sârbi Revisited. Grammaticalization and Language Contact. Contributions to the 24th Annual Scientific Conference of the Association of Slavists (Polyslav). 2023. 360-369
Kenta Sugai. On the Language Situation of Taraclia (Moldova) Through the Prism of Linguistic Landscape. Алманах "Българска украинистика". 2021. 10. 114-127
Kenta Sugai. Contemporary Language Situation in Parcani, Moldova. Contributions to the 23rd Annual Scientific Conference of the Association of Slavists (Polyslav). 2021. 343-352
Kenta Sugai. Book Review (Ruselina Nicolova, Bulgarian Grammar (Translated from Bulgarian by Assoc. Prof. Dr. Christo Stamenov) (Berlin: Frank & Timme GmbH, Verlag für wissenschaftliche Literatur, 2017), 714 pp.). Acta Slavica Iaponica. 2020. 40. 288-290
Kenta Sugai, Maria Chalakova. Negation, Adjectives and Compound Sentences of Adnominal Modification in Bulgarian. Journal of the Institute of Language Research (Tokyo University of Foreign Studies). 2019. 23. 145-150
Kenta Sugai. Field Research of Bulgarian Dialects in Romania. Slavia Iaponica. 2019. 22. 152-161
Sugai Kenta. Bulgarian (Data, Special Issue : "Transitivity"). 2014. 19. 253-263
The Suffix -'askă as an Integration Marker of Romanian Loan Verbs in the Bulgarian Dialect of Brăneşti
(Fundamentals and Advances in Balkan Linguistics 2023)
Някои проблеми относно учебните материали по български за японци (Some problems about the teaching materials of Bulgarian))
(Международна научна конференция "Българистика по света. Филологията у дома" (The International Conference "Bulgarian Studies Abroad. Philology at Home")) 2023)