Albeit Kotaro's unwillingness to admit that he cares deeply for Sakura, it has been shown throughout the series, as described by Yugiri, on how he is “especially kind to her (Sakura)” compared to the rest of Franchouchou.

Who is Kotaro to Sakura?

It has been confirmed that Kotaro is Sakura's friend after she calls him “Inui Kun.” According to Epic Dope, this revelation may have something to do with Sakura's death. Kotaro seems to have a feeling toward her and it can be seen in the tension between the two.

Does Kotaro know Sakura?

Episode 12

It is revealed that Kotaro used to be Sakura's classmate under the name of "Inui", where Sakura couldn't recognize him as he got older and it is possible that "Kotaro Tatsumi" is an alias he used in the entertainment industry.