谊

Left speech radical (side-form of 言) — the indexing radical. Pictograph of a mouth with a tongue protruding, abbreviated to two strokes. Anchors 谊 in the speech/social-interaction family with 说 speak, 话 talk, 论 discuss, 谈 chat. Friendship is expressed through speech and dialogue, a fitting choice.

Right 宜 supplies the sound yí → yì with tone shift, an exact rime match. Contributes faint meaning too: 宜 means 'fitting, appropriate, harmonious,' and friendship is precisely a fitting, harmonious bond between people. Same phonetic root family includes 谊 (this entry) and 妯 sister-in-law.