This is honestly the best conversation between Karamatsu and Osomatsu, and possibly the best conversation between Karamatsu and any of his brothers I will fight you about this.
Examples on why:
Karamatsu asking his big brother questions it’s cute
Osomatsu gigging and making jokes cuties
Osomatsu telling him too not worry about what others think
The birthplace of the Karamatsu tank top and the sinful man, guilt guy™
Osomatsu telling Karamatsu that he doesn’t need to change who he is or what he enjoys
Karamatsu looking genuinely happy/relieved at this
THE PEACEFULNESS AT THE END AHAHAHAHAHH
in short: the eldest brothers relationship is very pure and underrated.