@Nathy its mentioned in the beginning! but only hinted...(holiday?? sorry english is not my first language...but the time when kanna, gakane and yuder stay behind to train ):)
Spoiler!
yuder mentions or rather thinks that the reason gakane also stayed behind when they were allowed to leave for a holiday was to train with kanna! pretty sure it also mentions him glancing and blushing shortly... but nothing too hinting.
Spoiler!
lesbians unite
please do recommend me stuff<3